Ecological responses to blue water MPAs

Abstract

Marine protected areas (MPAs) can contribute to protecting biodiversity and managing ocean activities, including fishing. There is, however, limited evidence of ecological responses to blue water MPAs. We conducted the first comprehensive evaluation of impacts on fisheries production and ecological responses to pelagic MPAs of the Pacific Remote Islands Marine National Monument. A Bayesian time series-based counterfactual modelling approach using fishery-dependent data was used to compare the temporal response in the MPAs to three reference regions for standardized catch rates, lengths, trophic level of the catch and species diversity. Catch rates of bigeye tuna, the main target species (Kingman/Palmyra MPA, causal effect probability >99% of an 84% reduction; 95% credible interval:-143%,-25%), and blue shark (Johnston MPAs, causal effect probability >95%) were significantly lower and longnose lancetfish significantly higher (Johnston MPAs, causal effect probability >95%) than predicted had the MPAs not been established, possibly from closing areas near shallow features, which aggregate pelagic predators, and from 'fishing-the-line'. There were no apparent causal impacts of the MPAs on species diversity, lengths and trophic level of the catch, perhaps because the MPAs were young, were too small, did not contain critical habitat for specific life-history stages, had been lightly exploited or experienced fishing-the-line. We also assessed model-standardized catch rates for species of conservation concern and mean trophic level of the catch within and outside of MPAs. Displaced effort produced multi-species conflicts: MPAs protect bycatch hotspots and hotspots of bycatch-to-target catch ratios for some at-risk species, but coldspots for others. Mean trophic level of the catch was significantly higher around MPAs, likely due to the aggregating effect of the shallow features and there having been light fishing pressure within MPAs. These findings demonstrate how exploring a wide range of ecological responses supports evidence-based evaluations of blue water MPAs.

Bycatch Estimates From a Pacific Tuna Longline Fishery Provide a Baseline for Understanding the Long-Term Benefits of a Large, Blue Water Marine Sanctuary

“…However, given the historical differences in catch rates, species composition and spatial overlap between the LBF and DWF, future assessments of the PNMS may benefit, alongside other methods of census, from dedicated research fishing trips by the LBF in areas of the PNMS where fishing effort was once concentrated. Alternatively, a counterfactual approach could be used to assess the responses of various species to the PNMS by predicting what the LBF's catch would have been, had the designation of the sanctuary and the re-location of the DFZ not eliminated its fishing grounds (Gilman et al, 2020).…”

“…The local abundance of prey resources may have increased within the MPAs as a result of the cessation of fishing mortality, while at a "control" penguin colony with no MPA there may have been increased fishing mortality due to displaced fishing effort from the MPAs (Sherley et al, 2018). Second, a counterfactual assessment found that the U.S. Pacific Remote Islands Marine National Monument caused a reduction in blue shark catch rates by Hawaii's pelagic longline fishery (Gilman et al, 2020). The Monument was also found to have protected bycatch hotspots for some at-risk species (oceanic whitetip, silky and blue sharks, and olive ridley sea turtle) but cold spots for others (albatrosses, shortfin mako shark and striped marlin).…”

Area‐based management of blue water fisheries: Current knowledge and research needs

“…• Mean trophic level of the catch of Hawaii's tuna longline fishery was significantly higher around the U.S. Pacific Remote Islands Marine National Monument than at open ocean fishing grounds (i.e. a larger proportion of the pelagic community that is susceptible to capture in pelagic longline gear in the Monument is made up of top predators than in open ocean areas), suggesting that that the Monument contains a relatively undisturbed pelagic community structure (Gilman et al, 2020) Provide economic benefits • MPAs within the Great Barrier Reef, some of which include pelagic habitat, led to a 35%-36% reduction in catch and ex-vessel value (Fletcher et al, 2015), however, this conclusion is complicated by additional measures to reduce fishing capacity (Hughes et al, 2016 finding that social outcomes arise even in remote MPAs, they arise at all stages, can produce outcomes at a higher level of social organization, and can produce social change processes that lead to social impacts. These social effects of the MPAs may be intended or unintended, positive or negative (Gruby et al, 2017) Real-time, dynamic spatial management…”

“…Protect non-target species • A counterfactual assessment found that the U.S. Pacific Remote Islands Marine National Monument caused a reduction in blue shark catch rates by Hawaii's pelagic longline fishery (Gilman et al, 2020). The Monument was also found to have protected bycatch hotspots for some at-risk species (oceanic whitetip (Caracharhinus longimanus, Carcharhinidae), silky (Carcharhinus falciformis, Carcharhinidae) and blue sharks, and olive Ridley sea turtle (Lepidochelys olivacea, Cheloniidae)) but cold-spots for others (albatrosses (Phoebastria spp., Diomedeidae), shortfin mako shark (Isurus oxyrinchus, Lamnidae) and striped marlin; Gilman et al, 2020) • Small MPAs adjacent to African penguin (Spheniscus demersus, Speheniscidae) colonies that removed purse seine fishing for pelagic forage fishes may have improved penguin foraging efficiency, chick survival and condition, and increased population growth at one of the colonies.…”

“…The local abundance of prey resources may have increased within the MPAs as a result of the cessation of fishing mortality, while at a "control" penguin colony with no MPA there may have been increased fishing mortality due to displaced fishing effort from the MPAs (Pichegru et al, 2010(Pichegru et al, , 2012Sherley et al, 2015Sherley et al, , 2018 • During a court-ordered area closure of Hawaii's swordfish longline fishery, established to protect marine turtles, there was an increase in swordfish catch by non-U.S. longline fleets that had higher turtle bycatch rates than the U.S. swordfish fishery (Chan & Pan, 2016) • A hypothetical closed area for the U.S. Northwest Atlantic swordfish longline fishery located in a hotspot of pelagic species richness and density was simulated to reduce catch levels of some pelagic sharks and teleosts without reducing swordfish catch levels (Baum et al, 2003) • One existing and two hypothetical Mexican MPAs that ban gillnet fishing were simulated to cause an increase or at least slow the rate of decline of vaquita porpoise (Phoceana sinus, Phocoenidae) abundance (Gerrodette & Rojas-Bracho, 2011) Protect critical habitats • The "Mackerel Box" off Southwestern England reduced juvenile mackerel mortality (Sweeting & Polunin, 2005) • A seasonal closure to purse seine fishing in an area of the Eastern Pacific Ocean may have reduced juvenile bigeye tuna catch rates (IATTC, 2017) • Theoretically, restricting pelagic fishing at shallow submerged features could reduce catch rates of juveniles of target tuna species (Adam et al, 2003;Fonteneau, 1991;Gilman et al, 2020;Sibert et al, 2000) • 85% of the foraging habitat around breeding colonies of three species of tropical boobies (Sula spp., Sulidae) were within two U.S. closed areas (Young et al, 2015). There may have been indirect benefits to the booby populations from removing tuna longline fishing in the MPAs.…”