Abstract
Depredation of southern rock lobster (Jasus edwardsii) within fishing gear by the Maori octopus (Pinnoctopus cordiformis) has economic and ecological impacts on valuable fisheries in South Australia. In addition, depredation rates can be highly variable resulting in uncertainties for the fishery. We examined how in-pot lobster predation was influenced by factors such as lobster size and sex, season, fishing zone, and catch rate. Using mixed modelling techniques, we found that in-pot predation risk increased with lobster size and was higher for male lobsters. In addition, the effect of catch rate of lobsters on predation risk by octopus differed among fishing zones. There was both a seasonal and a spatial component to octopus predation, with an increased risk within discrete fishing grounds in South Australia at certain times of the year. Information about predation within lobster gear can assist fishery management decision-making, potentially leading to significant reduction in economic losses to the fishery.
Highlights
Predation plays an integral role in marine ecosystems influencing the structure and dynamics of ecological communities, with direct effects on prey populations via density-dependent mechanisms, as well as indirect effects through altering prey behaviour and physiology ([3])
Given that temporal changes in lobster size have been documented in both fishing zones (Fig 1), we developed a generalized linear mixed model (GLMM) including year as a random intercept, which was nested by zone to reduce the temporal and spatial variability of predictors
The effect of lobster catch rate or CPUE on in-pot predation risk varied among marine fishing areas (MFAs), with significant effects in MFAs 15, 28, 39 from the northern zone (NZ) and MFA 55 in the southern zone (SZ) (p
Summary
Predation plays an integral role in marine ecosystems influencing the structure and dynamics of ecological communities, with direct effects on prey populations via density-dependent mechanisms (e.g. predator responses [1,2]), as well as indirect effects through altering prey behaviour and physiology ([3]). Predation is considered as a pervasive but ephemeral feature [4] and represents a large source of fish mortality, which in many cases, exceeds fishing mortality [5]. Predators are able to interact directly with fisheries by preying upon target species caught within fishing gear, mortality known as ‘depredation’ [6]. Information about predator–fishery interactions have been mostly reported from top predator depredation in long-line fisheries [7,8,9]. Depredation can occur in a variety of fishery systems, including trap-based fisheries for lobster and crab where teleosts (e.g. conger eels, [10]), elasmobranchs (e.g. catsharks,[11]), and cephalopods (e.g. octopus, [12,13]) are common middle-trophic predators within fishing gear. In contrast to depredation from top predators, PLOS ONE | DOI:10.1371/journal.pone.0139816 October 21, 2015
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