Development of a new control rule for managing anthropogenic removals of protected, endangered or protected species in marine ecosystems

Rhona Rodger
Wednesday 11 January 2023
Date: 19 April 2023
Time: 2:00 pm

Speaker: Matthieu Authier, Pelagis Observatory, France

Title: Development of a new control rule for managing anthropogenic removals of protected, endangered or protected species in marine ecosystems

Abstract: By-catch, the unintentional catch of other species during fishing operations targeting commercial species, is a major threat to many marine Protected, Endangered or Threatened Species (PETS) including cetaceans. The aim of this work was to propose a new rule for managing anthropogenic removals of PETS, compared to existing rules. We developed a stochastic SPM model (Surplus Production Model) which includes abundance and removal processes, linked to each other under the assumption that variations in removals reflect variations in abundance. By-catch and abundance are linked by a removal rate (ϕ). The three other parameters of the stochastic SPM are: the intrinsic growth (r), the carrying capacity (K) and an environmental stochasticity (σ). A simulation study was carried out under the SPM to investigate (1) the sensitivity of population extinction to {ϕ, r, σ}, and (2) parameter identifiability from typical data that can be collected on PETS.

We then consider several control ’harvest’ rules to manage PETS by-catch, included two new ones from this SPM model. The two new rules hinge on the estimation of a stationary removal rate (ϕ). We compared these new rules to other existing control rules (e.g. Potential Biological Removal or a fixed percentage rule) in three scenarios: (i) a base scenario whereby unbiased but noisy data are available, (ii) scenario whereby abundance estimates are overestimated and (iii) scenario whereby abundance estimates are underestimated. The different rules were tested on a simulated set of data with life-history parameters close to a small-sized cetacean species, the Harbour Porpoise (Phocoena phocoena) and in a MSE (Management Strategy  Evaluation) framework. The effectiveness of the rules were assessed by looking at performance metrics, such as time to reach the conservation objective, the removal limits obtained with the rules or temporal autocorrelation in removal limits. One new rule relying on the SPM model and the trend in abundance was robust against biases in data and displayed greater alignment with EU conservation objectives. This new rule is promising and could be used in the management of marine mammals by-catch, such as the common dolphin (Delphinus delphis) in the Bay of Biscay.

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