Commercial fisheries bycatch mortality rates

I was discussing commercial fishing operations over the weekend while visiting family in Siletz. The conversation involved questions about how significant are the impacts of bycatch and release on fish mortality rates.

These questions arose after the presentation of an anecdote about a group of recreational fishers who took a trip out from Newport to catch some salmon recently. The fishers were not allowed to take hatchery-raised fish, which can be identified because of a clipped fin. So, they had to throw back twenty illegal fish in the process of catching the four legal fish. One point of the story was that the fish that were released during this trip would be tired and wounded; wouldn't these fish then be less likely to survive once they've been thrown back in the water?

This question implied an affirmative answer, and the implication, in my understanding, was to suggest that current state and federal fisheries management practices were not effective. A further, more subtle implication, I believe, was that the state and federal governments should not regulate fisheries, but should let individual sports and recreational fishers regulate themselves.

I will save for another post my commentary on the implied (libertarian) conclusions of the question, but the original question was quite compelling. My immediate response was that it seemed certain that there would be scholarship on this topic—these research findings may not be widely known beyond academics and specialists, but I was sure that people have researched this exact topic.[1] In this post, I've provided some research I've uncovered after conducting a quick search through the academic literature.

I found a large amount of peer-reviewed research on the topic of bycatch mortality. I first searched for the terms "fish* bycatch mortality" using Google Scholar, and got about 16,700 hits.[2] I conducted a second Google Scholar search using the terms "salmon bycatch mortality" and got about 5,520 hits.

Below I've listed some representative examples of the range of sources I found on only the first two pages of hits from both of these searches. This range include experimental studies, broader industry analyses, and literature reviews.

Based upon the abstracts of the sources cited below, the following points seem to summarize effectively the state of knowledge on the topic of bycatch mortality rates:

** "A broad-based public consensus has emerged that bycatch should be minimized to levels approaching insignificance. This view, as reflected in U.S. and worldwide legislation and agreements, demonstrates the widely held belief that discarded portions of fishery catches . . . represent an unacceptable waste of natural resources."[3]

** "The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide."[4]

** "the connections between physiological stress and mortality in bycatch processes remain to be fully understood."[5]

** "Generally, the proper application of the careful release techniques results in only minor hook removal injuries. . . not all fish judged . . . as likely to die actually die."[6]

** "inadequate data [exist] to determine biological, ecological, economic, and cultural impacts of discards although economic losses run to billions of dollars. However, it appears most likely that socio-cultural attitudes towards marine resources will guide international discard policies."[7]

I've linked to these sources below and indicated my research methods so that anyone can follow-up with these materials to come up with their own conclusion. My conclusion is that there is not a clear 1:1 correlation between caught-and-released fish and mortality rates; that what correlation does exist varies with the fishing methods and species of fish; that society has recently become more aware of bycatch mortality and is beginning to demand changes; that specialists are conducting research on the topic to minimize bycatch/catch-and-release mortality; and that mortality rates will only decrease significantly when socio-cultural attitudes change and these attitudes become manifest in modified fishing practices spurred, to an important degree, by state, federal, and international regulations.

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[1] One of these days, I'll write a post lamenting the lack of availability of much research beyond the rather limited population of those people who have access to databases and academic journals. I see at least two conflicting dynamics involved in this issue: First, in our current system, databases and academic journals need to rely on paid subscriptions to maintain their operations; however, society-at-large ought to benefit from the research produced by specialists. My opinion is that society-at-large does not benefit nearly as much as it should from peer-reviewed research because society's prioritization of economic considerations over knowledge that would help foster an engaged democratic citizenry.

[2] The asterisk (*) at the end of the word "fish" in the search terms broadens the search beyond the root word. In this case, the search would be broadened to include "fish," "fishes," "fishing," "fished," "fishery," and "fisheries."

[3] Crowder, "Fisheries Bycatch: Implications for Management."

[4] Davis, "Key principles for understanding fish bycatch discard mortality."

[5] Davis, et al, "Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish."

[6] Kaimmer and Trumble, "Injury, condition, and mortality of Pacific halibut bycatch."

[7] Alverson, A global assessment of fisheries bycatch and discards.

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Sources

Dayton L. Alverson, et al., A global assessment of fisheries bycatch and discards (Rome: FAO Fisheries Paper 339, 1994).

Summary: Authors estimate that between 17.9 and 39.5 million tons of fish are discarded each year in commercial fisheries. The highest quantities of discards are from the Northwest Pacific while tropical shrimp trawl fisheries generate a higher proportion of discards than any other fishery type, accounting for one third of the global total. Authors compare bycatch death rates of trawls, purse seines, drift nets, long-lines, and pot fisheries. Authors point to inadequate data to determine biological, ecological, economic, and cultural impacts of discards although economic losses run to billions of dollars. However, it appears most likely that socio-cultural attitudes towards marine resources will guide international discard policies.

Larry B. Crowder, "Fisheries Bycatch: Implications for Management," Fisheries 23 (1998), 8-17.

Abstract: A broad-based public consensus has emerged that bycatch should be minimized to levels approaching insignificance. This view, as reflected in U.S. and worldwide legislation and agreements, demonstrates the widely held belief that discarded portions of fishery catches (including economic resources, protected species, and unobserved mortalities of animals not caught) represent an unacceptable waste of natural resources. Bycatches in their various forms can have significant consequences for populations, food webs, and ecosystems. The economic effects of bycatches can influence not only the levels of yields to individual fisheries, but also may have major effects on allocations among competing fisheries. The lack of comprehensive monitoring programs in most areas to assess bycatches and integrate them into population and multispecies models seriously impedes a full understanding of bycatch consequences and the efficacy of measures for their amelioration. Nevertheless, where evidence for significant bycatches exists, a risk-averse and perhaps adaptive management philosophy is clearly warranted. Establishing the benefits and costs associated with bycatch management is a priority as managers attempt to define the practicality of bycatches approaching zero given the institutional, scientific, and industry resources necessary to accomplish the job.

R. Berghahn, M. Waltemath, and A. D. Rijnsdorp, "Mortality of fish from the by-catch of shrimp vessels in the North Sea," Journal of Applied Icthyology 8:1-4 (Aug. 1992),293–306.

Abstract: Results from three different programmes concerning by-catch mortality in shrimp fisheries. Mortalities increased considerably after the catch passed the sorting sieve. 100% mortality detected for whiting (Merlangius merlangus). Mortalities were about 10% for sculpin (Myxocephalus scorpius), hooknose (Agonus catapbractus), and eelpout (Zoarces viviparus). Survival of flatfish depended strongly on the species, the size of the specimens as well as the catch and catch processing conditions, and ranged from 17 to 100%.

Michael W. Davis, "Key principles for understanding fish bycatch discard mortality," Canadian Journal of Fisheries and Aquatic Sciences 59:11 (2002), 1834–1843.

Abstract: The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide. Development of accurate measures of discard mortality requires fundamental knowledge, based on principles of bycatch stressor action, of why discarded fish die. . . . The discard mortality problem is best addressed through a combination of laboratory investigation of classes of bycatch stressors to develop knowledge of key principles of bycatch stressor action and field experiments under realistic fishing conditions to verify our understanding and make predictions of discard mortality. . . .

M. W. Davis, B. L. Olla, and C. B. Schreck, "Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: lack of concordance between mortality and physiological measures of stress," Journal of Fish Biology 58:1 (Jan. 2001), 1–15.

Abstract: In a series of laboratory studies designed to simulate bycatch processes, sablefish Anoplopoma fimbria were either hooked for up to 24 h or towed in a net for 4 h and then subjected to an abrupt transfer to elevated sea water temperature and air. Mortality did not result from hooking or net towing followed by exposure to air, but increased for both capture methods as fish were exposed to elevated temperatures, reflecting the magnifying effect of elevated temperature on mortality. . . . The results suggest that caution should be exercised when using physiological measures to quantify stress induced by capture and exposure to elevated temperature and air, that ultimately result in mortality, since the connections between physiological stress and mortality in bycatch processes remain to be fully understood.

Michael W. Davis and Steven J. Parker, "Fish Size and Exposure to Air: Potential Effects on Behavioral Impairment and Mortality Rates in Discarded Sablefish," North American Journal of Fisheries Management 24 (2004), 518-524.

Abstract: Fisheries models often assume that discarded undersized fish and target species will survive and contribute to future recruitment and yield. If smaller fish are more susceptible to capture stressors than larger fish, then the assumption that smaller discards would contribute to recruitment may not be true. We tested the hypothesis that small sablefish Anoplopoma fimbria show more behavioral impairment and mortality than large fish when exposed to air (10–60 min) at various temperatures (10–18°C). Sablefish captured by trawl, longline, or trap are commonly exposed to these conditions during warmer seasons when brought up on deck and sorted. Two size-classes of fish . . . were used in the experiments. . . . Small fish mortality increased as air time increased and was at higher levels than in large fish. Only 10 min of air exposure caused behavioral impairment in small and large fish, which could lead to increased predation on discarded fish. At 24 h after air exposure, normal behavior had not generally resumed and small fish had more behavioral impairment than large fish.

Anthony P. Farrell, Patricia E. Gallaugher, and Richard Routledge, "Rapid recovery of exhausted adult coho salmon after commercial capture by troll fishing," Canadian Journal of Fisheries and Aquatic Sciences 58:12 (2001), 2319–2324.

Abstract: To reduce mortality in the by-catch of commercial salmon fisheries, techniques are being explored to revive fish before live release and improve survival. By measuring blood and muscle variables, we demonstrated that capture of coho salmon (Oncorhynchus kisutch) by commercial trolling methods resulted in severe exhaustion and stress . . . Nevertheless, coho salmon recovered rapidly by swimming in a cage alongside the vessel while fishing activity continued. . . . There was no postcapture delayed mortality after 24 h. Therefore, we have established that postexhaustion activity promotes a rapid recovery in wild salmon and this result might find application in nonretention commercial and recreational fishing.

Stephen M. Kaimmer and Robert J. Trumble, "Injury, condition, and mortality of Pacific halibut bycatch following careful release by Pacific cod and sablefish longline fisheries," Fisheries Research 38:2 (Oct. 1998), 131-144.

Abstract: Pacific halibut caught as bycatch or intended for discard by longline vessels in US and Canadian waters of the north Pacific must be removed from the hook using careful release techniques required by regulation. In many fisheries, trained observers subsample the released halibut for fish condition. These condition codes are used to track cumulative bycatch mortality in these fisheries. Tag return rates of halibut released from longline gear near Kodiak Island, Alaska, are used to estimate relative and absolute mortalities of fish by release method, hook removal injury, and condition code. Generally, the proper application of the careful release techniques results in only minor hook removal injuries. Survival rates of moderately and severely injured halibut are 1.5–2 times higher than previously assumed. One result of our study is the finding that not all fish judged at tagging as likely to die actually die. We recommend a reworking of the condition code methodology.

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