Shooting fish in a barrel? Assessing fisher‐driven changes in catchability within tropical tuna purse seine fleets

Tidd, Alex; Brouwer, S. L.; Pilling, Graham M.

doi:10.1111/faf.12207

Cited by 22 publications

(16 citation statements)

References 40 publications

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“…; Tidd et al. ). The differential degree to which this occurs in the angling and spearing fisheries was evident in the β parameters of these relationships for each fishery (spearfishing: β = 0.41, which shows more hyperstability and less self‐regulation; angling: β = 0.53, which shows less hyperstability and more self‐regulation).…”

Section: Discussionmentioning

confidence: 99%

“…; Tidd et al. ). Under such circumstances, and as evidenced by some degree of self‐regulation in each fishery, responsive angler and spearfisher behavior should act to stabilize regional fisheries when numerous fishing opportunities exist.…”

Section: Discussionmentioning

confidence: 99%

“…) and angler and fleet innovation (Tidd et al. ). As the stock declines, the area occupied by that stock shrinks, generally to concentrate in optimal habitat areas, and anglers and spearfishers can target a larger proportion of the remaining stock per unit of effort depending on angler or spearfisher experience, skill, and innovation (Walters and Martell ; Ward et al.…”

Section: Discussionmentioning

confidence: 99%

“…; Tidd et al. ). Relationships between catch and harvest rate and density aid in determining the gradient of self‐regulation (catch rates change proportionally with population size) and hyperstability (catch rates remain elevated when population declines) in a fishery (Ricker ; Hansen et al.…”

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confidence: 99%

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Characterizing the Angling and Tribal Spearing Walleye Fisheries in the Ceded Territory of Wisconsin, 1990–2015

Mrnak

Shaw

Eslinger

et al. 2018

N American J Fish Manag

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Assessment of the Walleye Sander vitreus angling and tribal spearing fisheries in the Ceded Territory of Wisconsin (CTWI) is critical for the sustainability of this resource. Key to these assessments is an understanding of harvest demographics, exploitation, catch and harvest efficiency, and relationships between catch or harvest and adult density. We characterized the size distribution and mean length of harvested Walleyes, harvest, exploitation rate, and catch (angling) or harvest (spearing) rate for both fisheries during 1990-2015. Then, we evaluated catch and harvest rates in relation to adult density and tested for self-regulation or hyperstability in each fishery. Size distribution and mean length of harvested Walleyes in both fisheries were statistically different but biologically similar. Anglers harvested significantly more Walleyes, and the mean exploitation rate was greater in the angling fishery. Spearfishers had significantly higher mean harvest rates compared with angler catch rates. Catch and harvest rates followed an asymptotic relationship with adult density, with the spear fishery showing more hyperstability than the angling fishery. In the CTWI, naturally reproducing Walleye populations are managed for densities ≥7.4 adults/ha. Our results suggest that maintaining adult Walleye densities near the point of diminishing returns of the asymptotic relationship (10-15 Walleyes/ha) will result in a sustainable fishery that also maximizes tribal harvest and angler catch. However, maintaining adult Walleye densities within this range in the unproductive lakes typical of the CTWI may be unrealistic. Due to the hyperstability observed in each fishery, active management of the spear fishery should continue and monitoring of the angling fishery should also continue given recent declines in natural recruitment and production observed in the CTWI in order to maintain Walleye populations in a "safe operating space." An empirical understanding of CTWI Walleye angler and spearfisher effort dynamics is critically needed to mechanistically explain the observed hyperstability in each fishery.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Characterizing the Angling and Tribal Spearing Walleye Fisheries in the Ceded Territory of Wisconsin, 1990–2015

Mrnak

Shaw

Eslinger

et al. 2018

N American J Fish Manag

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“…The EEZ dFAD retention times we have calculated here demonstrate an alternative spatial measure of fishing effort to days fishing or number of sets made. Assuming that the number of dFADs in an area is related to fishing strategy and success, then a method of combining simulated dFAD trajectories with available dFAD position data may provide a standardised density covariate for understanding changes in catchability and CPUE in purse seine fleets targeting tuna (Lopez et al 2015, Tidd et al 2017. The access to currently incomplete dFAD tracking data has already indicated the potential influence of high dFAD densities to CPUE in these fisheries (Escalle et al 2018b).…”

Section: Management Implicationsmentioning

confidence: 99%

Regional connectivity and spatial densities of drifting fish aggregating devices, simulated from fishing events in the Western and Central Pacific Ocean

Phillips

Escalle

Pilling

et al. 2019

Environ. Res. Commun.

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The increased use of drifting Fish Aggregating Devices (dFADs) by tuna purse seine fleets in recent years has supported considerable catches of these species. A greater understanding of the spatiotemporal dynamics of these objects as they drift with ocean currents is critical for understanding historical changes in fishing power, spatial management, and examining the effect of ambient dFAD density on catch and effort. Here, dFAD dynamics were estimated for all floating object sets made by purse seiners in the Western and Central Pacific Ocean during 2016 and 2017. The drift trajectories of these floating objects prior to the observed fishing events were estimated by seeding virtual Lagrangian particles within a state-of-the-art hydrodynamics model, and simulating their movements backwards in time. Resulting trajectory distributions are similar to observed dFAD trajectories from the same period. The approach provides spatial density estimates in areas where observed dFAD data are incomplete, particularly in the exclusive economic zone (EEZ) of Howland and Baker Islands, and certain high seas areas. We provide estimates of inter-EEZ connectivity of dFADs, which highlight the fact that dFADs set upon in small EEZs such as Nauru and Howland and Baker Islands are likely to have drifted from neighbouring EEZs less than one month prior to fishing. dFADs typically transited multiple EEZs, with a median of 4 and a maximum of 14, when assuming a drift-time of six months. Moreover, between 4 and 22% of dFAD sets made in the WCPO were estimated to have originated from the Eastern Pacific Ocean, depending on drift-time. We examine our results in the context of the improved management and assessment of dFAD fisheries, providing a methodology to estimated relative dFAD density over historical periods to support analyses of catch and effort. The sensitivity of these estimates to hydrodynamic models, including the proposed SKIM doppler radar altimetry method, is discussed.

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Implications of life history uncertainty when evaluating status in the Northwest Atlantic population of white shark (Carcharodon carcharias)

Bowlby

Gibson

2020

Ecology and Evolution

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To effectively protect at‐risk sharks, resource managers and conservation practitioners must have a good understanding of how fisheries removals contribute to changes in abundance and how regulatory restrictions may impact a population trajectory. This means they need to know the number of animals being removed from a population and whether a given number of removals will lead to population increases or declines. For white shark (Carcharodon carcharias), theoretical quantities like the intrinsic rate of population increase or rebound potential (ability to increase in size following decline) are difficult to conceptualize in terms of real‐world abundance changes, which limits our ability to answer practical management questions. To address this shortfall, we designed a simulation model to evaluate how our understanding of longevity and life history variability of white shark affects our understanding of population trends in the Northwest Atlantic. Then, we quantified the magnitude of removals that could have caused historical population declines, compared these to biologically based reference points, and explored the removal scenarios which would result in population increase. Our results suggest that removals on the order of 100s of juveniles per year could have resulted in population‐level declines in excess of 60% during the 1970s and 1980s. Conservation actions implemented since the 1990s would have needed to be nearly 100% effective at preventing fishing mortality in order for the population to double in abundance over the last 30 years. Total removals from all fleets needed to be exceptionally small to keep them below biological reference points for white shark in the Northwest Atlantic. The population's inherent vulnerability to fishing pressure reaffirms the need for restrictive national and international conservation measures, even under a situation of abundance increase.

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Shooting fish in a barrel? Assessing fisher‐driven changes in catchability within tropical tuna purse seine fleets

Cited by 22 publications

References 40 publications

Characterizing the Angling and Tribal Spearing Walleye Fisheries in the Ceded Territory of Wisconsin, 1990–2015

Characterizing the Angling and Tribal Spearing Walleye Fisheries in the Ceded Territory of Wisconsin, 1990–2015

Regional connectivity and spatial densities of drifting fish aggregating devices, simulated from fishing events in the Western and Central Pacific Ocean

Implications of life history uncertainty when evaluating status in the Northwest Atlantic population of white shark (Carcharodon carcharias)

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