Ignoring the spatial structure of the sea cucumber Isostichopus fuscus distribution when granting quotas can be costly

Abstract

There is an increasing demand for fisheries resources worldwide. For example, the Asian markets have traditionally consumed sea cucumber as a delicacy and their buoyant economies have promoted demand for it in recent years. The brown sea cucumber Isostichopus fuscus is the most valuable species from the Eastern Pacific and it has been almost depleted due to overfishing. In this work, we analyzed data of sea cucumber abundance collected monthly (October 2014–December 2016) along the west coast of the Gulf of California (29.95 oN – 28.05 oN) in 1,107 swath (25 × 2 m) quadrats performed at 118 sites with the goal of determining if current fishing quotas are sustainable. We applied a Bayesian hierarchical modelling approach with integrated nested Laplace approximation (INLA) to this data to account for spatial structure in the data when calculating densities. The observed density ranged from a minimum of 0 to a maximum of 0.58 ind/m2, with an average of 0.03 ind/m2 in suitable habitat, defined as the habitat less than 30 m deep and with hard substrate. There are large spatial variations in abundance, but the overall mean suitable habitat is 15.7% (min = 7.8%, max = 28.8%) of the total fishing area. Current quotas are usually higher than 5% of the lower bounds of population density estimates. We propose, among other management measures, that quotas should be granted taking into account the spatial structure of sea cucumber densities as well as the proportion of suitable area within each estate. Given the high levels of illegal fishing within the Gulf of California, it is imperative that quotas are based on the lower bounds of spatially explicit density estimates – along with increased surveillance and enforcement – if the long-term commercial sustainability of the fishery is to be maintained.

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ORCID for Felix Eigenbrod: orcid.org/0000-0001-8982-824X

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