Chinook Salmon Bycatch Research Articles

Warm oceans exacerbate Chinook salmon bycatch in the Pacific hake fishery driven by thermal and diel depth‐use behaviours

AbstractFisheries bycatch impacts marine species globally and understanding the underlying ecological and behavioural mechanisms could improve bycatch mitigation and forecasts in novel conditions. Oceans are rapidly warming causing shifts in marine species distributions with unknown, but likely, bycatch consequences. We examined whether thermal and diel depth‐use behaviours influenced bycatch of a keystone species (Chinook salmon; Oncorhynchus tshawytscha, Salmonidae) in the largest fishery on the US West Coast (Pacific hake; Merluccius productus, Merlucciidae) with annual consequences in a warming ocean. We used Generalized Additive Models with 20 years of data including 54,509 hauls from the at‐sea hake fishery spanning Oregon and Washington coasts including genetic information for five salmon populations. Our results demonstrate that Chinook salmon bycatch rates increased in warm ocean years explained by salmon depth‐use behaviours. Chinook salmon typically occupy shallower water column depths compared to hake. However, salmon moved deeper when sea surface temperatures (SSTs) were warm and at night, which increased overlap with hake and exacerbated bycatch rates. We show that night fishing reductions (a voluntary bycatch mitigation strategy) are effective in reducing salmon bycatch in cool SSTs by limiting fishing effort when diel vertical movements bring salmon deeper but becomes less effective in warm SSTs as salmon seek deeper thermal refugia during the day. Thermal and diel behaviours were more pronounced in southern compared with northern salmon populations. We provide mechanistic support that climate change may intensify Chinook salmon bycatch in the hake fishery and demonstrate how an inferential approach can inform bycatch management in a changing world.

Coded-Wire Tag Sampling: The Case for Electronic-Field Detection

A clipped adipose fin served as an effective external mark indicating presence of a coded-wire tag (CWT) in salmon (Oncorhynchus spp.) from the 1960s until the mid 1990s when hatcheries in the Pacific Northwest began mass marking released fish with an adipose fin clip, but not necessarily a CWT. Since then, many CWT sampling programs of commercial fisheries have transitioned to electronic-field detection, while others are still visual-field only, examining snouts from all adipose-clipped salmon, even those without CWTs. Because some CWT salmon are released from hatcheries without any external marks, visual-field only programs also fail to sample these CWTs. In 2012, we used electronic tag detection at a processing plant in Kodiak, Alaska, to scan 1,201 Chinook salmon (O. tschawytscha) caught as bycatch in the US North Pacific groundfish fisheries in the Gulf of Alaska (GOA). Chinook salmon bycatch were also electronically scanned in partnerships with private industry: 3,713 salmon in the 2013–2016 US rockfish fishery in the central GOA, and 611 salmon in testing of salmon excluder devices in 2013 in the central GOA groundfish fisheries. Electronic-field detection increased CWT recovery rates by 20–24% over visual-field detection of adipose-clipped Chinook salmon, and an estimated 64–74% of adipose-clipped Chinook salmon sampled had no CWTs. Visual-field only CWT sampling programs may unnecessarily process large numbers of untagged, adipose-clipped salmon while also recovering fewer CWTs than comparable electronic sampling programs.

The effect of artificial illumination on Chinook salmon behavior and their escapement out of a midwater trawl bycatch reduction device

The Pacific hake (Merluccius productus) midwater trawl fishery is the largest groundfish fishery off the U.S. West Coast by volume. Catches comprise mainly Pacific hake, however, bycatch of Chinook salmon (Oncorhynchus tshawytscha) can be an issue affecting the fishery as Endangered Species Act (ESA) listed Evolutionarily Significant Units represent a portion of the total Chinook salmon bycatch. We conducted two separate experiments evaluating the influence of artificial illumination on Chinook salmon behavior and their escapement out a bycatch reduction device (BRD) in a Pacific hake midwater trawl. In Experiment 1, we tested whether Chinook salmon could be attracted out specific escape windows of a BRD equipped with multiple escape windows using artificial illumination. In Experiment 2, we compared Chinook salmon escapement rates out of the BRD between tows conducted with and without artificial illumination to determine if illumination can enhance their escapement. Our results show that artificial illumination can influence where Chinook salmon exit out of the BRD, but also demonstrate that illumination can be used to enhance their escapement overall. As conservation of ESA-listed Chinook salmon is an ongoing management priority, our research contributes new information on how artificial illumination can minimize adverse interactions between the Pacific hake fishery and Chinook salmon.

Comprehensive incentives for reducing Chinook salmon bycatch in the Bering Sea walleye Pollock fishery: Individual tradable encounter credits

After record salmon bycatch in 2007 by the Eastern Bering Sea and Aleutian Islands fishery for walleye Pollock, the North Pacific Fishery Management Council (NPFMC) concluded that additional management strategies were necessary to further control salmon bycatch. The Preliminary Preferred Alternative (PPA) was selected in April 2009 and implemented in January 2011 as Amendment 91. In this paper, we present the original comprehensive bycatch credits allocation and trading plan as designed by the first author as commissioned by the Alaskan Pollock Fleet for Chinook salmon, the Comprehensive Incentive Plan (CIP). The CIP, which uses individual (vessel-level) tradable encounter credits (ITEC), included incentives that make up the backbone of Amendment 91/PPA. While salmon bycatch has been reduced since the implementation of the PPA, the current amendment does not have individual vessel incentives that vary with the vulnerability of salmon populations. The CIP approach presented here provides robust vessel-level incentives to reduce Chinook salmon bycatch under all levels of salmon abundance, but particularly when salmon populations are at their lowest levels and are most vulnerable. The specific financial incentive structure in the full plan, with trading of by-catch liabilities among vessels, can be applied well in other fisheries where bycatch threatens both sustainability and profitability.

Genetic stock composition analysis of the Chinook salmon bycatch samples from the 2015 Gulf of Alaska trawl fisheries

Genetic stock composition analysis of the Chinook salmon bycatch samples from the 2015 Gulf of Alaska trawl fisheries

Estimating impacts of the pollock fishery bycatch on western Alaska Chinook salmon

Chinook salmon (Oncorhynchus tshawytscha) are taken as bycatch in the Bering Sea pollock (Gadus chalcogrammus) fishery, with recently revised management measures in place to limit the overall Chinook salmon catch. Historical impact of the bycatch on regional salmon stocks is made difficult because, until recently, sampling for the stock composition of the bycatch was patchy and diverse in approaches. In this study, extensive observer data on the biological attributes (size and age composition) of the bycatch were used to estimate the impact on specific regional stock groups (RSGs), as defined given available genetic stock identification estimates. Our model provides estimates of the impact on Chinook salmon RSGs, given seasonal and spatial variability in the bycatch, and accounts for observed in-river age compositions, uncertainty in age-specific oceanic natural mortality of Chinook salmon, and between-year variability in genetic information. The upper Yukon River stock is transboundary and subject to heightened management interest and international management agreements on escapement goals. Our study updates results from an earlier analysis used to develop the management regulations that went into place in 2011. It shows that the new data result in slight changes in previous estimates, and that the lower overall Chinook salmon bycatch since 2008 has resulted in lower impacts to the main western Alaskan RSGs.