Predicting changes in the catchability coefficient through effort sorting as less skilled fishers exit the fishery during stock declines

Poorten, Brett T. van; Walters, Carl J.; Ward, Hillary G. M.

doi:10.1016/j.fishres.2016.06.023

Cited by 41 publications

(28 citation statements)

References 42 publications

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“…In our study area we estimated the exploitation rate induced by anglers using fishery-independent data (underwater cameras) and a BACI design. Although exploitation rates could be directly estimated by mark and recapture studies observing tag returns of marked fishes by fishers39, estimating exploited biomass or abundance and associated reference points using fishery-dependent data notoriously difficult and costly40. In addition, conventional stock assessment approaches based on fishery-dependent data are prone to biases4142.…”

Section: Discussionmentioning

confidence: 99%

Fast and behavior-selective exploitation of a marine fish targeted by anglers

Alós

Palmer

Rosselló

et al. 2016

Sci Rep

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Harvesting of wild-living animals is often intensive and may selectively target heritable behavioral traits. We studied the exploitation dynamics and the vulnerability consequences of individual heterogeneity in movement-related behaviors in free-ranging pearly razorfish (Xyrichthys novacula). Using underwater-video recording, we firstly document a fast and high exploitation rate of about 60% of the adult population removed in just few days after the opening of the season. Subsequently, we tagged a sample of individuals with acoustic transmitters and studied whether behavioral traits were significant predictors of the vulnerability to angling. Tagged individuals revealed repeatable behaviors in several home range-related traits, suggesting the presence of spatial behavioral types. The individuals surviving the experimental fishery showed only localized and low-intensity movement patterns. Our study provides new insights for understanding the harvesting pressures and selective properties acting on behavioral traits of recreational fishing. Many fish stocks around the globe are today predominantly exploited by recreational fisheries. The fisheries-induced change in fish behavior described here may be therefore widespread, and has the potential to alter food-webs, profitability of the fisheries and to affect stock assessment by eroding catchability in the long-term.

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Section: Discussionmentioning

confidence: 99%

Fast and behavior-selective exploitation of a marine fish targeted by anglers

Alós

Palmer

Rosselló

et al. 2016

Sci Rep

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“…The trends at a boat level cannot be properly analyzed due to a confidentiality agreement, yet it will be very interesting to disentangle if the less efficient boats are those that are quitting the activity (fishers sorting). In this case, apparent stability of CPUE (landings per fishing trip) may mask a decrease in stock abundance (van Poorten et al, 2016). Alternatively, warning signs should not be deducted from stationary CPUE.…”

Section: Management Outcomesmentioning

confidence: 99%

“…However, this is in practice a more challenging goal than expected. The approaches used in the past to identify métiers either (i) make use of existing records on the technical features of fishing trips (e.g., gear and mesh size used, fishing grounds visited, season, boat characteristics), which may be available from fishers' logbooks, (Marchal et al, 2006;Ulrich et al, 2001), or inferred from interviews with fishers (Christensen and Raakjaer, 2006;Neis et al, 1999), or (ii) are intended to ascertain the métiers used by retrospectively examining the landings (Deporte et al, 2012;Marchal, 2008).…”

Section: Introductionmentioning

confidence: 99%

Combining sale records of landings and fishers knowledge for predicting métiers in a small-scale, multi-gear, multispecies fishery

et al. 2017

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Stock management should be guided by assessment models that, among others, need to be fed by reliable data of catch and effort. However, precise data are difficult to obtain in heterogeneous fisheries. Specifically, small-scale, multi-gear, multispecies fisheries are dynamic systems where fishers may lively change fishing strategy (i.e., métier) conditioned by multiple drivers. Provided that some stocks can be shared by several métiers, a precise categorization of métiers should be the first step toward métier-specific estimates of catch and effort, which in turn would allow a better understanding of the system dynamics. Here we propose an approach for predicting the métier of any given fishing trip from its landing records. This approach combines the knowledge of expert fishers with the existing sales register of landings in Mallorca (Western Mediterranean). It successfully predicts métiers for all the 162,815 small-scale fishery fishing trips from Mallorca between 2004 and 2015. The largest effort is invested in the métiers Cuttlefish/Fish and Spiny lobster, landings peak for Cuttlefish/Fish and Dolphinfish and revenues for Spiny lobster and Dolphinfish. Métier predictions also allowed us to describe the temporal (seasonal and between-year) trends experienced by each métier and to characterize the species (commercial categories) that are specific to each métier. Seasonal variability is by far more relevant than betweenyear variability, which confirms that at least some fishers are adopting a rotation cycle of métiers along the year. Effort (fishing trips), landings and gross revenues decreased in the last 12 years (2004 to 2015). The approach proposed is also applicable to any other fishery for which the métier for a fishing trip sample is known (e.g., on-board observers or logbooks), but relying on fishers expertise points more directly to fishers' intention. Thus, métier predictions produced with the proposed approach are closer to the actual uses of fishers, providing better grounds for an improved management.

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“…Interestingly, bag limits are often criticized because they lack precision in the ability to control harvest rates, even if the bag limit changes in response to population size (Andersen, 2015). In addition, concerns have been raised because the catchability coefficient seem to be inversely density dependent (Andersen and Kaltenborn, 2013;Eriksen et al, 2017) creating a risk that harvest rates become higher at low population densities (se e.g., from the fishery literature; Harley et al, 2001;Ward et al, 2013;van Poorten et al, 2016). It has been indicated that managers can achieve more control of offtake by allocating seasonal quotas to individual hunters or hunting teams (see e.g., Gibson et al, 2011), where the hunters/teams are allocated a given proportion of total area quota (see e.g., Kurki and Putaala, 2010).…”

Section: Limiting Total Allowable Catch (Tac)mentioning

confidence: 99%

Harvest Regulations and Implementation Uncertainty in Small Game Harvest Management

2017

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A main challenge in harvest management is to set policies that maximize the probability that management goals are met. While the management cycle includes multiple sources of uncertainty, only some of these has received considerable attention. Currently, there is a large gap in our knowledge about implemention of harvest regulations, and to which extent indirect control methods such as harvest regulations are actually able to regulate harvest in accordance with intended management objectives. In this perspective article, we first summarize and discuss hunting regulations currently used in management of grouse species (Tetraonidae) in Europe and North America. Management models suggested for grouse are most often based on proportional harvest or threshold harvest principles. These models are all built on theoretical principles for sustainable harvesting, and provide in the end an estimate on a total allowable catch. However, implementation uncertainty is rarely examined in empirical or theoretical harvest studies, and few general findings have been reported. Nevertheless, circumstantial evidence suggest that many of the most popular regulations are acting depensatory so that harvest bag sizes is more limited in years (or areas) where game density is high, contrary to general recommendations. A better understanding of the implementation uncertainty related to harvest regulations is crucial in order to establish sustainable management systems. We suggest that scenario tools like Management System Evaluation (MSE) should be more frequently used to examine robustness of currently applied harvest regulations to such implementation uncertainty until more empirical evidence is available.

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Predicting changes in the catchability coefficient through effort sorting as less skilled fishers exit the fishery during stock declines

Cited by 41 publications

References 42 publications

Fast and behavior-selective exploitation of a marine fish targeted by anglers

Fast and behavior-selective exploitation of a marine fish targeted by anglers

Combining sale records of landings and fishers knowledge for predicting métiers in a small-scale, multi-gear, multispecies fishery

Harvest Regulations and Implementation Uncertainty in Small Game Harvest Management

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