ifish article by cca member n Tide Mag debunks tangle nets

January 11th, 2009

To: Jack Smith – CCA Oregon GRC vice chairman
Ed Wickersham – CCA Washington GRC chairman

From: Brad Damm – CCA Oregon GRC member
Subject: Tangle net release mortality

Jack,

Pursuant to your request, I researched and investigated the 14.7% release mortality rate being used by fisheries managers in Oregon and Washington with regard to the use of tangle nets in the Columbia River spring Chinook commercial fishery and found the following:

The released spring Chinook mortality rate associated with the use of tangle nets is based on a 2003 recommendation of the US v. Oregon Technical Advisory Committee (TAC) from the recovery of Passive Induced Transponder (PIT) tags on one part of test netting done in 2003. Originally, in a memorandum to the Columbia River Compact (CRC) dated December 23rd, 2003 (based on incomplete tag data at the time), the Technical Advisory Committee recommended that the CRC adopt a point estimate of 18.5% (with a standard error of 1.4%) and estimate the 95% confidence interval at between 15.8% and 21.3% (LeFleur, 2003).

On March 3rd 2008, the TAC again met to consider the tangle net mortality rates. Apparently, some final data analysis was completed in late 2007 which resulted in small changes to recovery and release information from the 2003 PIT tag groups. Because of this, the TAC recommended reducing the mortality estimate from 18.5% to 14.7%. The mechanisms that resulted in this recommended reduction were not described in the memorandum dated March 26th, 2008 from the TAC to the CRC, and my understanding is the CRC did adopt the 14.7% mortality rate, and that rate that was used in the 2008 tangle net commercial fishery.

There are several possible shortcomings with this methodology.

2003 Control Groups Mortality

There were 2 control groups used in 2003. One control group of spring Chinook salmon was released at the Bonneville Dam fish trap and one was released downriver in the area the test netting was done. The TAC used only the downriver control group in the original estimate of 18.5%. Using the control group released at the dam would have increased the mortality rate of the tangle net fish to more than 18.5%, but the TAC felt that these fish had a ‘survival advantage’ that the tangle net fish did not have being released several miles below the dam (LeFleur, 2003). The TAC decided that the differential survival [mortality] between the upstream released control group and the tangle net fish was too high and thus discounted the upstream control group. No specific scientific reason was given by the TAC for doing so.

In actuality, scientific study (Bromaghin et.al, 2004) has shown that holding migrating adult salmon for as little as 4 hours increases overall long term mortality rates and negatively affects migration. The downstream control group fish were held up to 24 hours prior to release which would presumably give the downstream control group an artificially increased mortality. This would (in turn) decrease the differential survival between the control group chosen by the TAC and the tangle net released fish (which were not held for significant lengths of time prior to release) suggesting that the actual mortality rate for the tangle nets should have been be greater than 18.5% originally and should now be greater than 14.7%.

Additionally, the area immediately below Bonneville Dam contains the highest concentrations of marine mammals in the lower Columbia River. The downstream control group favored by the TAC would had to migrate through this area twice and would have been subjected the twice the opportunity for marine mammal predation versus the tangle net released fish that only migrated thru this area once (Ashbrook, 2008). A second migration through the area immediately below the dam, after being subjected to the stress and loss of energy reserves from their first migration below and thru the dam, would have made the downstream control group more susceptible to marine mammal predation on their second trip through the area between the release site and the base of the dam. The principal investigator in 2003 even noted a “dinner bell effect” where certain Sea lions quickly learned to anticipate the arrival of the hatchery truck transporting the downstream control group at the two downstream release sites (Ashbrook, 2008). The only conceivable reason for these Sea Lions to be aware of and await the arrival of the hatchery truck would be that the downstream control group fish made easy targets for predation immediately following their release. Again, this would likely decrease the differential survival between the downstream control group and the tangle net released fish, which clearly suggests more mortality attributable to tangle nets than would have been accounted for by the TAC estimate.

Hydroelectric dams are formidable obstacles to upstream migrating salmon, and there are some losses of upstream adult migrants at each hydroelectric dam on the Columbia River. Presumably upstream migrating fish get injured passing the dams, get tired, and some percentage just never find the fish ladders (FERC, 2008). For the purposes of the 2003 study, the downstream released control group had to pass one the equivalent of one additional hydroelectric project during the course of their 2003 migration. They pass through Bonneville twice, followed in turn by each dam upstream once. The upstream control group and the tangle net group only had to pass Bonneville once, followed by the upstream dams once. Being subjected to passing what amounts to one additional major hydroelectric dam would clearly have also artificially decreased the differential survival of the downstream control group in the 2003 calculations as compared to the either the upstream control group or the tangle net study group. As noted above, an artificial decrease in control group survival can only suggest a larger tangle net mortality than the current 14.7% calculated by the TAC.

The principal investigator of the 2003 study shares these concerns in her 2008 thesis and recommends that fisheries managers use the upstream control group mortality results in fisheries management decisions (Ashbrook, 2008).

Also, it is worthy to note that for the purposes of estimating mortality attributable to tangle nets during an actual commercial fishing season, a true control is unattainable with any of the methodology used in 2003. Some control group mortality would result from trapping the fish, anestistizing them, attaching jaw tags and implanting PIT tags, etc… A true comparison for fisheries management purposes would measure the mortality of adult fish migrating upstream completely unmolested versus fish migrating upstream after being captured in and released from tangle nets. This would likely require massive PIT tagging of spring Chinook as juveniles to eliminate control group mortality from trapping and tagging the fish as adults.

2001-2002 Previous Data Mortality

According to its memorandum in 2003, the TAC apparently discounted the data from 2002 (LeFleur, 2003) that suggested a higher average release mortality rate than 18.5% (currently adjusted to 14.7%) because of the lower detection rate of the jaw tags used in those years. The release mortality rate in 2002 was a 34.6%, and the 2001-2002 average was a release mortality rate of 20.6%. This suggests release mortality from tangle net encounters is highly variable from year to year, and measured across multiple years it would be larger than was measured in 2003. The TAC felt that since PIT tags were more likely to be detected at the dams the 2003 data would be the most accurate. Yet valid scientific controls were used in the previous two years and problems in detecting or recovering jaw tags would have affected both the control groups and the study groups equally. As such, there would have been no scientifically valid reason for the TAC to discount the jaw tag data spanning 3 years of returns with valid scientific controls in favor of one year of PIT data in 2003. By doing so, the TAC decreased the sample size over both time (one year vs. three years) and numbers of fish sampled (eleven hundreds vs. several thousand) making the resultant mortality estimate statistically less accurate.

Since the previous years of jaw tag returns vary widely and would indicate an average mortality (20.6% average common point estimate, 95% CI) in excess of the one year PIT tag mortality range (12.0%-17.4%, 95% CI), it is more likely than not that the common point estimate of 14.7% from 2003 was a result of conditions specific to the year 2003 and not indicative of the overall long term mortality average of fish released from tangle nets over multiple years. The 2001-2002 jaw tag results when combined with the 2003 PIT tag results can only suggest an overall higher average release mortality than 14.7%, had it been measured across multiple years.

Increased Wild Fish Mortality

When captured in hook and line fisheries, behavioral differences between wild (natural origin) and hatchery reared fish are often noted by experienced anglers. Wild fish are typically more aggressive, tending to fight harder and struggle longer than similar hatchery fish. The current TAC estimate of 14.7% release mortality from was derived from 2003 releases of both hatchery and natural origin fish. It is noted in the WDFW tangle net evaluation (VanderHagen et. al, 2002) that there may be a higher mortality to natural origin fish captured in tangle nets than to hatchery fish captured in tangle nets. In the course of the 2001 research netting less than half (43%) of the fish captured in were unmarked, yet more of the fish killed (56%) during their encounter with the tangle nets were unmarked. Later lab analysis confirmed that ten out of eleven unmarked fish were of natural origin. This indicates that wild fish will have a higher mortality than hatchery fish in tangle nets.

Since only unmarked fish are released in commercial fishing operations, using a mix of both marked and unmarked fish in estimating tangle net release mortality would be inaccurate in a real commercial fishery. If wild fish are more susceptible to death in tangle nets than hatchery fish, and since only unmarked fish are released during normal commercial fishing, the release mortality attributable to tangle net use in an actual commercial fishery should be greater than the current 14.7% point estimate recommended by the TAC, as their estimate is based on results of research netting using the assumption that both wild and hatchery fish have similar survival following a tangle net encounter.

Upriver Delayed Mortality

The data from 2003 used by the TAC in originally estimating mortality rates at 18.5% is based only on PIT detections at Columbia River dams during migration, and did not include any estimate of long term mortality that could have occurred upstream of the hydropower system. The TAC reasoned that most mortality from the use of tangle nets occurs within the short term and says short term mortality estimates are “adequate” for fishery management decisions. No estimate at all of any long term mortality was included in the original 18.5% calculation. (LeFleur, 2003)

Virtually every adult Chinook salmon captured in tangle nets will have net mark injuries around its snout or in some cases its body and loss of the protective slime layer associated with this injury makes the fish more susceptible to disease, especially Saphrolegnia spp. fungus (VanderHagen et. al, 2002). This appears as a condition where much of the head or body of the fish is covered with a thick white layer often impairing vision and swimming ability and is common in post-spawn dying salmon. Columbia River spring Chinook salmon generally enter the river about 4-5 months prior to spawning, osmoregulate, and then must successfully navigate the river. Technical staff at the dams following the 2002 test fishery noted and photographed fungus on fish that had been tagged as part tangle net study in the area of the nose and snout where a tangle net would have typically captured Chinook salmon (Ashbrook, 2008). The fungus documented at net injury locations was on pre-spawn fish still in migration and would likely increase the mortality (prior to spawning) associated with tangle net injuries. Such fungus and disease would not have been observed by PIT tag detection and would suggest a delayed mortality greater than the original 18.5% (now 14.7%) estimated by the TAC.

At initial capture and again at release fish in the study groups (fish captured by tangle nets) were rated on a scale of 1-5 as follows (VanderHagen et. al, 2002): “A fish was initially ranked as condition 1 if it was lively and not bleeding, condition 2 if it was lively but bleeding, condition 3 if it was lethargic but not bleeding, condition 4 if it was lethargic and bleeding, and condition 5 if it showed no visible movement or ventilation.” Fish ranked condition 1 or 2 were tagged and released overboard immediately. Fish in conditions 3 to 5 were held in the recovery boxes until they either recovered to condition 1 or 2 and could be released, or they died. The jaw tag test netting results show fish initially captured in condition 1 were disproportionally represented in the recovered tags over fish captured in conditions 3-5 and apparently recovered to condition 1 before release. While 91.4% of the tags recovered were from fish that were considered to be in condition 1 at capture, only 82.6% of the fish themselves were considered to be in condition 1 at capture (VanderHagen et. al, 2002). This result clearly supports a hypothesis that not all tangle net release mortality occurs in the short term and that there is at least some long term delayed mortality that occurs as a result of tangle net capture and release.

Overall, the tag recovery data clearly indicates that although recovery box revived spring Chinook may appear recovered to a good condition at release, physiologically they will not all fully recover in the near term as assumed by the TAC in their December 23rd, 2003 memorandum to the Columbia River Compact. It seems likely that there are long term detrimental physiological factors to salmon from tangle net encounters that are not yet fully understood. If so, they could only increase the overall mortality to something greater than the 14.7% (originally 18.5%) mortality estimated by the TAC.

Lower River Fishing Mortality

The early tangle net studies clearly show an increasing mortality rate for tangle and gill nets the further downstream from Bonneville Dam the test netting was done (VanderHagen et. al, 2002). As salmon enter freshwater from the ocean, they go through physiological changes and appear to survive encounters with tangle nets and gillnets at a greater rate if they have been in fresh water for a longer period of time prior to capture or have migrated further upstream at the time of capture.

In order to coordinate in river treatment and control groups, the test netting in 2003 was done in an small area centered only about 21 km below Bonneville Dam near Beacon Rock (Ashbrook, 2008). Bonneville Dam is 235 km upstream from the Pacific Ocean. Most commercial netting is done in the lower 100 km of the river where mortality rates would very likely be greater than the 14.7% estimated by the TAC (based only on 2003 test netting that was done more than 100 km further upstream) and outside of the lower river tidally influenced area that the bulk of the commercial fishery occurs in.

Tangle Net Dropout Mortality

For the purposes of the 2003 study used by the TAC to estimate tangle net mortality, it is assumed that every fish captured by the nets is taken onboard the boat, observed, and tagged with either a PIT tag or Jaw tag (Ashbrook, 2008). None of the 2001-2003 tangle net studies attempts to make any estimate at all of dropout mortality.

The Pacific Salmon Commission estimates a Chinook salmon dropout mortality rate of 3% for Columbia River gillnet commercial fisheries (JCTC, 1997). It seems reasonable that a tangle net would experience a dropout rate in excess of a gill net and some mortality would occur as a result of such dropouts. Any mortality at all from uncounted or unseen dropouts could only increase the overall tangle net mortality to something greater than the 14.7% estimated by the TAC.

Pinniped Mortality

The immediate and post mortality estimate from the 2003 study includes some, but not all Sea Lion predation (C. E. Ashbrook, personal communication, 2009). It is noted in the 2003 study that all immediate mortalities observed were due to Sea Lion predation in the net. Sometimes during the course of netting parts of fish were recovered as the net was pulled in, but the researchers believe there were also very likely fish taken that the observers never saw because they were completely pulled out prior to the net being recovered. No estimate of fish completely removed from the nets during the study was ever included in the mortality calculation. Out of 1173 fish captured by the tangle nets in 2003, 25 could not be revived, and all as a result of pinniped predation that occurred while the fish were held trapped in the nets (Ashbrook, 2008).

Pinnipeds were observed at nearly three quarters (71.6%) of all sets during 2003 tangle net tests, and 68.5% of the time when the test netting captured Chinook salmon there was at least one fish recovered with a marine mammal injury, yet only 25 dead fish (or parts of dead fish) were recovered in tangle nets during test netting. This clearly suggests that some fish were completely removed from the nets, and the actual loss to pinnipeds is far greater than is accounted for in the point estimate of 14.7% in the current TAC recommendation. No estimate of these types of unseen pinniped losses is included in the 2003 study or the original 18.5% recommendation.

In addition, the population of Sea Lions present in the lower Columbia River has grown each year since tangle nets were studied. According to USACE counts, there were 6 Sea Lions present in the area below Bonneville Dam in 2001. By 2003 (the year of the study used by the TAC to estimate tangle net mortality) there were 31 Sea Lions present in the same area during the spring Chinook migration, and by 2006 the population at the dam had grown to over 100 individuals (ODFW, 2008).

It seems obvious that the increase in the number of Sea Lions present in the lower Columbia River during spring Chinook salmon migration would also increase the overall mortality from Sea Lion predation in net fisheries. There has been no adjustment to the tangle net mortality rate assumed by the TAC to account for well over a threefold increase in the number of pinnipeds present in the lower Columbia River during recent commercial fishing seasons. More pinnipeds present in the fishing area now than when the test netting was done in 2003 would increase the mortality from tangle nets to greater than the 14.7% calculated from the 2003 test netting results, perhaps dramatically.

Soak Time Mortality

There is an obvious and well documented relationship between soak times and net related mortality for salmonids (Hargreaves et. al, 2001). It has been concluded that mortality rates increase rapidly with increasing soak time, and short soak times (first cork in to last cork out) are likely required to achieve low mortality rates. In the test fishery, researchers chose the appropriate soak time (Ashbrook, 2008) to minimize mortality rates on released fish. In the 2003 test netting using tangle nets, the average soak time was 34 minutes (Ashbrook, 2008).

In a real world commercial fishery soak times are chosen by boat captains to maximize catch rates. The current regulatory limit for soak time in Columbia River commercial fishing is 45 minutes; however, there are multiple violations most years where the soak times of commercial fishers exceed 45 minutes. The use of tangle nets also increases the soak time as compared to a conventional gill net. The tangle net captures many more non target species than a conventional gill net and this increases soak time as it takes longer to remove the non-salmonids from the net. In the early tangle net studies, the occurrence of dead salmon in the net was related to the total number of non-salmonids captured. Sets with dead adult spring Chinook had significantly more non-salmonids (VanderHagen et. al, 2002). The occurrence of non-salmonids and steelhead is likely greater in the lower river and estuary (where most commercial fishing takes place) than in the confined area directly below Bonneville where the 2003 test netting took place which would very likely increase average soak times.

The mortality point estimate currently used by the TAC of 14.7% is based only on the 2003 test fishery where soak times averaged 34 minutes and contains no adjustment for the increased soak time permitted by law of 45 minutes. Additionally, the mortality estimate recommended by the TAC has not been adjusted for documented soak times in real Columbia River commercial tangle net fishing operations that can be in excess of 70 minutes (The Daily Astorian, 2007). This clearly suggests the actual mortality of real commercial fishing operations is greater than the 14.7% recommended by the TAC for tangle net management in 2008.

Post Release Behavior

The salmon released from the tangle nets in the 2003 study took longer to migrate between dams and also took longer to pass each dam than the control groups used in 2003 in nearly every instance (Ashbrook, 2008). Taking a longer time to migrate and pass hydroelectric dams likely increases the mortality on the fish released from tangle nets. They would be exposed to greater predation, greater fishing pressure, and warmer water temperatures later in the season. It has been shown that increased temperature contributes to adult passage delay that may result in permanent straying to downstream sites or migration failure (FERL, 2008). The average temperature in the Columbia River was 10-15% less than normal during the spring and summer of 2003 (NOAA, 2009). In a year with average or above average water temperatures the longer migration noted by the 2003 tangle net research would likely further increase passage time, resulting in increased mortality and causing greater straying and migration failure than was calculated in the 2003 research. If this is true, the mortality estimate of 14.7% presumed by the TAC would only be valid in years with lower than average water temperatures in the Columbia River during the spring and summer. In years with average or higher than average water temperatures, mortality would be greater than 14.7% and would likely also increase over time with any trend towards global warming.

Fish Handling and Enforcement

The authors of a 2002 net release mortality study on the Skeena River note that some combination of changes to economic incentives, education, monitoring, and enforcement will be needed to achieve the low mortality in seen in research fisheries. Major reductions in net mortality [rates] have only been achieved with educated crews trained in the use of short soak times and careful fish handling. Economic incentives to process target species may well interfere with the motivation and ability to handle incidentally caught salmon. (Buchanan et. al, 2002)

In the 2003 Columbia River study used by the TAC to estimate tangle net mortality, fishing crews were paid for fishing and not by the fish caught in an effort to ensure careful fish handling (Ashbrook, 2008). Due to ESA restrictions in the mainstem Columbia River commercial fishery, there are a very few very short open times and locations each year to fish. The clear economic incentive is for commercial fisherman is to make as many sets as possible in as short of a time as possible to maximize the number of fish caught during the short open season. The same commercial fishers hired by WDFW to conduct the 2003 test fishery later pled guilty to over 50 separate violations of falsifying fish records during regular Columbia River commercial fishing seasons in 2005-2007 (AP, 2009). One has to question if any data accumulated by or with their participation could be tainted, thus causing the overall research project to be unreliable or lacking in scientific integrity.
Typical commercial fisheries also often occur at night making observation and careful fish handling impossible. For example, in the 2003 test fishery crews fished in the daytime and were asked to look over the bow of the boat and locate fish in the net prior to being brought onboard and then were required to carefully lift the fish over the bow roller whenever possible to minimize injury. Obviously this would not be possible in a typical nighttime commercial fishery. In addition, researchers were onboard each boat at all times during 2003 to ensure fishermen did not lapse in careful fish handling techniques, using revival boxes, fishing with appropriately sized nets (purchased with research funds), and using shorter soak periods. Observers are not currently required and are not typically present to ensure similar careful fish handling behavior during a real Columbia River commercial fishing operation.

According to the principal investigator of the 2003 test fishery, these ideal circumstances for ensuring spring Chinook salmon survival in test fisheries cannot be expected of all the fishermen in the midst of an actual fishery, and no further advances in reducing tangle net mortality are likely to be achieved in the future (Ashbrook, 2008). It seems very clear that mortalities from the actual circumstances, methods, and economics present in real world Columbia River tangle net commercial fishing and would exceed the 14.7% release mortality estimate adopted from the results of the 2003 test fishery.

Spawning Success

Stress response in fish reduces reproductive success. (Schrek et. al, 2000). As such, even though adult spring Chinook salmon may survive capture and release from tangle nets, there may be physiological effects that would reduce reproductive success. Since the whole point of a mark selective fishery is to release natural origin ESA listed fish to presumably spawn future generations of weak stocks that need protection, there should obviously be consideration given to reproductive success (or lack thereof) in the mortality estimates used for tangle net fisheries.

Research done with Willipa Bay Coho in the fall of 2003 indicated that the progeny of adults released from gillnets survived at a rate 5.6% worse than the progeny of fish released from tangle nets at the eyed egg to fry stage of development. (Ashbrook, 2008) Although there was no natural origin control group to compare to, this result is significant as it tends to indicate there is at least some differential decrease in the reproductive success of adult salmon that are released from net fisheries. This research was unavailable to the TAC at the time they recommended the original 18.5% mortality rate. It is very significant because their current 14.7% mortality calculation assumes that, of the 85.3% of adult spring Chinook that they believe survive release from tangle nets, 100% of those fish go on to spawn as successfully as natural origin fish that did not encounter a tangle net during their upstream migration. If there is any differential in reproductive success between fish that were released from a tangle net and those that did not encounter a tangle net, it has the same net effect as if the mortality rate had been greater than 14.7%. In terms of successive generation juvenile recruitment for the original calculation, a mere 10% differential in reduced reproductive success would have the same overall effect as if the adult mortality rate was increased by 8.53%.

Because spring Chinook salmon enter the river months before spawning, it is expected that any potential survival impacts to their progeny will be greater than that imparted to species that enter freshwater shortly before spawning such as Coho salmon (Ashbrook, 2008).

Conclusions

Upon review of all the data available to me, I believe that the tangle net mortality rate of 14.7% used in main stem management decisions by the Columbia River Compact is artificially low. It clearly represents a ‘best case’ scenario that is achievable only by fisheries biologists in very controlled conditions that had been designed to be favorable to the survival of released tangle net fish. The integrity of the commercial fishermen participating in the research can be called into question, and the study methodology uses several assumptions that are not true in real Columbia River commercial fishing. The calculations do not include any representation or estimate of several known aspects of tangle net release mortality. It also does not provide for possible long term physiological effects on survival or reproductive success that would negatively influence the conservation benefits intended from of the use of this type of gear.

Many of the possible problems with the methodology used by the US v. Oregon Technical Advisory Committee in assessing tangle net release mortality are mentioned in the above pages and citations are provided for your review where appropriate. Please note that even though the singular effect of any one of these issues or omissions could perhaps be relatively small, the overall cumulative effect of all these issues on the mortality of spring Chinook salmon released from tangle nets could be great. For example, if each problematic issue described above were to only affect the presumed TAC tangle net mortality rate by as little as 5%, the cumulative effect of all those small errors could easily double the release mortality estimate. It is clear these issues exist, and the scientific community has cautioned fisheries managers on the limitations of research test fisheries on numerous occasions. Just because some of these known limitations may not be easy to quantify is certainly no reason to ignore them, especially in a weak stock management regime where endangered wild salmon and steelhead are mixed with abundant hatchery fish.

In my opinion, the areas of greatest uncertainty and concern are dropout mortality, pinniped mortality, fish handling in a ‘real world’ unmonitored commercial fishery, and potential reproductive failure as a result of tangle net encounters. I would urge the Oregon GRC to adopt a position encouraging fisheries managers to be conservative with mortality estimates used in management decisions in tangle net fisheries until these issues have been researched and are better understood. Until such time as that happens, I would recommend CCA advocate for a presumed mortality of no less than 30% for tangle net released salmon, such that any errors made in fish management decisions are on the side of conservation of our valuable ESA listed stocks.

Other Findings

Also worthy of note is that the test fishing from 2001-2002 (designed to compare mortality rates from tangle nets to gillnets) clearly demonstrated an overall mortality rate in excess of 50% for the use of conventional 8” drift gillnets (VanderHagen et.al, 2002). In actuality, the mortality rate demonstrated could be higher than 50% as this test netting was another ‘best case’ scenario, with careful handling of released fish, the use of recovery boxes, and even a low incidence of pinnipeds. Because the 2003 study groups did not involve the use of conventional gillnets, the 2001-2002 results are very likely the best, the most current, and the most relevant science available to estimate spring Chinook release mortality from the use of conventional 8” mesh drift gillnet gear on the Columbia River below Bonneville Dam.

This is interesting because as late as 2004 the Columbia River Compact had assigned a mortality rate of 40% to releases of unmarked spring Chinook from lower river gillnets (CRC, 2004). It is noted from 2004 that the CRC based this rate on the recommendation of the US v. Oregon Technical Advisory Committee at that time. The mortality rate for conventional gillnets has not been reviewed since 2004 that I am aware of, and it is my understanding that the assumption of a 40% release mortality is still what is used for fisheries management decisions in the various conventional lower river gillnet fisheries to this day.

In light of the less than 50% jaw tag recovery when using when using conventional commercial 8” mesh gillnets (under close to ideal conditions for survival and adjusted for valid scientific controls) in the 2002 comparison test netting, the assigned release mortality rate for conventional gillnets needs to be re-examined and increased from 40% to at least 50% at the earliest opportunity. This should be of special concern since in recent years the CRC has often preferred the use of conventional gillnets in the early season lower river fisheries when there is a high probability of ESA listed steelhead encounters.

It seems inconsistent that the TAC would use ‘best case’ study results from test netting to recommend mortality rates for use in fisheries management when those results indicate a lower mortality rate for tangle nets, yet at the same time completely ignore ‘best case’ test netting results when they clearly indicated the release mortality rate for conventional large mesh gillnets was significantly higher than had previously been assumed.

A Final Note

We should applaud the various scientists and researchers who have spent years looking for better and more selective harvest methods to help save our wild ESA listed stocks of salmon and steelhead. There should be a large distinction made between the direct results of scientific study, and how those results are often applied in fisheries management decisions that are often fueled by political, social, and economic considerations.

The dedicated people doing the scientific research are often limited in their inquiries by circumstances and funding decisions beyond their control. The integrity of the scientists doing the research is exemplified by the fact that nearly every research paper regarding net mortality contains a fair assessment of the limitations of the research and its limitations in the real world of managing our fisheries. Their studies often caution fisheries managers about what is still unknown with regard to net mortality and may contain recommendations make for further research. We should all listen to their warnings and support their future efforts.

Sincerely,

Brad Damm, Oregon GRC member.

__________________
I dont give a damn for a man that can only spell a word one way. - Mark Twain

Uglygreen
View Public Profile
Send a private message to Uglygreen
Find More Posts by Uglygreen
Add Uglygreen to Your Contacts
Uglygreen Donation Stats

06-29-2009, 09:01 PM #8
Uglygreen
Sturgeon

Join Date: Aug 2002
Location: Tigard, Oregon
Posts: 4,390 Re: "Tangled In Controversy"

--------------------------------------------------------------------------------

The references cited...

Quote:

References
LeFleur, C. December 23rd, 2003. Memorandum to Bill Tweit and Steve King; Recommendation for Tangle Net Mortality Rate. Washington Department of Fish and Wildlife Intergovernmental Resource Management, 600 Capitol Way, Olympia, WA, 98501-1091

U.S. v Oregon Technical Advisory Committee. March 26th, 2008. Recommendations for Tangle Net release mortality assumptions for Spring Chinook. Washington Department of Fish and Wildlife, 600 Capitol Way, Olympia, WA, 98501-1091

Bromaghin, J. F. and T. J. Underwood. 2004. Evidence of residual effects from the capture and handling of Yukon River fall chum salmon in 2002. U. S. Fish and Wildlife Service, Alaska Fisheries Technical Report Number 70, Anchorage, Alaska.

VanderHagen, G.E., K.W. Yi, C.E. Ashbrook, E.W. White and L.L. LeClair. 2002. Evaluate Live Capture Selective Harvest Methods. Washington Department of Fish and Wildlife, 600 Capitol Way, Olympia, WA, 98501-1091

C.E. Ashbrook. 2008. Selective Fishing and Its Impact on Salmon: A Tale of Two Test Fisheries. University of Washington School of Fisheries and Aquatic Sciences, 1122 NE Boat Street, Seattle, WA 98105

Joint Chinook Technical Committee. 1997. Incidental Fishing Mortality of Chinook Salmon: Mortality Rates Applicable to Pacific Salmon Commission Fisheries. Pacific Salmon Commission, 600-1155 Robson St., Vancouver, B.C. Canada, V6E 1B5

ODFW Fish Division. Management of Sea Lion Predation on Threatened and Endangered Salmonids. 2008. Oregon Department of Fish and Wildlife, 3406 Cherry Avenue NE, Salem, OR 97303

N. B. Hargreaves and C. Tovey. 2001. Mortality Rates of Coho Salmon Caught by Commercial Salmon Gillnets and Effectiveness of Revival Tanks and Reduced Soak Time for Decreasing Coho Mortality Rates. Fisheries and Oceans Canada, Science Branch, Stock Assessment Division, Pacific Biological Station, Nanaimo, B.C. Canada. V9T 6N7

The Daily Astorian. April 4, 2007. Two gillnetters cited for keeping nets in too long. The Astorian Budget Publishing Co. 949 Exchange Street, Astoria, OR 97103

Fish Ecology Research Lab (FERL). 2008 (ongoing). A study of the probability of adult Chinook salmon and steelhead passing through the Hydrosystem and successfully spawning in the Snake River drainage, given exposure to variable temperature regimes during migration from the ocean. University of Idaho, CNR Rm 103, Moscow, ID 83844

US Department of Commerce, National Oceanic and Atmospheric Administration (NOAA). 2009. Recorded Columbia River Temperature Archive. National Weather Service, Portland Office, 5241 NE 122nd Avenue, Portland, OR 97230-1089

S. Buchanan and A.P. Farrell, J. Fraser, P. Gallauhger, R.J. Routledge and R Routledge. 2002. Reducing Gill-Net Mortality of Incidentally Caught Coho Salmon. North American Journal of Fisheries Management 22:1270-1275. American Fisheries Society, 5410 Grosvenor Lane, Bethesda, MD 20814

Associated Press (AP). January, 22nd, 2009. Brothers to pay $150,000 in fishing fines. Salem Statesman Journal. 280 Church Street NE, Salem, OR 97309

Schreck, C.B., W. Contreras-Sanchez and M.P. Fitzpatrick. 2001. Effects of stress on fish reproduction, gamete quality and progeny. Aquaculture 197:3-24.

Columbia River Compact (CRC). March 18th, 2004. Joint Staff Report – Winter Fact Sheet No. 9. Oregon and Washington Departments of Fish and Wildlife. http://www.dfw.state.or.us/fish/OSCR...arch18fact.pdf