96 research outputs found
Shining a light on the composition and distribution patterns of mesophotic and subphotic fish communities in Hawai‘i
As agencies shift from single-species management to ecosystem-based fisheries
management, ecosystem models are gaining interest for understanding species dynamics in relation
to oceanographic and ecological processes and human marine uses. However, information on
community structure or distribution of many species that occupy deep (>30 m) waters is largely
unavailable. We amassed a total of 24 686 fish observations of 523 species/taxa for the 30−410 m
depth areas surrounding the main Hawaiian Islands (MHI). We also obtained estimates of geomorphological
variables, including substrate type, slope, rugosity, and ridge-like features. Using these
2 data sources, we (1) identified distinct fish communities along the 30−410 m depth gradient, and
(2) generated relative biomass maps for fish functional groups. We showed that the mesophotic
zone ranges between 30 and 129 m, with a fish faunal break at 60 m. Beyond this zone, 4 subphotic
zones were identified: upper rariphotic (130−169 m), mid-rariphotic (170−239 m), lower rariphotic
(240−319 m), and upper bathyal (320−410 m). We assigned fish species to functional groups partly
based on identified depth ranges and fitted general additive models (GAMs) integrating geomorphological
covariates to the functional group relative biomass estimates to determine the environmental
variables that best predict the probability of encounter and relative biomass of each fish
functional group. Finally, GAM predictions were employed to map functional group relative biomass
distributions. These distribution maps showed a high relative biomass of many groups in the
center of the MHI chain. This study contributes to a better understanding of fish community structure
around the MHI and will inform ecosystem model parameterization
Relative Impacts of Adult Movement, Larval Dispersal and Harvester Movement on the Effectiveness of Reserve Networks
Movement of individuals is a critical factor determining the effectiveness of
reserve networks. Marine reserves have historically been used for the management
of species that are sedentary as adults, and, therefore, larval dispersal has
been a major focus of marine-reserve research. The push to use marine reserves
for managing pelagic and demersal species poses significant questions regarding
their utility for highly-mobile species. Here, a simple conceptual
metapopulation model is developed to provide a rigorous comparison of the
functioning of reserve networks for populations with different admixtures of
larval dispersal and adult movement in a home range. We find that adult movement
produces significantly lower persistence than larval dispersal, all other
factors being equal. Furthermore, redistribution of harvest effort previously in
reserves to remaining fished areas (‘fishery squeeze’) and fishing
along reserve borders (‘fishing-the-line’) considerably reduce
persistence and harvests for populations mobile as adults, while they only
marginally changes results for populations with dispersing larvae. Our results
also indicate that adult home-range movement and larval dispersal are not simply
additive processes, but rather that populations possessing both modes of
movement have lower persistence than equivalent populations having the same
amount of ‘total movement’ (sum of larval and adult movement spatial
scales) in either larval dispersal or adult movement alone
Diel Variations in Survey Catch Rates and Survey Catchability of Spiny Dogfish and their Pelagic Prey in the Northeast US Continental Shelf Large Marine Ecosystem
This study examines the potential uncertainty in survey biomass estimates of Spiny Dogfish Squalus acanthias in the Northeast U.S. Continental Shelf Large Marine Ecosystem (NES LME). Diel catch-per-unit-effort (CPUE) estimates are examined from the Northeast Fisheries Science Center bottom trawl surveys conducted during autumn (1963-2009) and spring (1968-2009). Influential environmental variables on survey catchability are identified for Spiny Dogfish life history stages and five pelagic prey species: Butterfish Peprilus triacanthus, Atlantic Herring Clupea harengus, shortfin squid Illex spp., longfin squid Doryteuthis spp., and Atlantic Mackerel Scomber scombrus. Daytime survey catchability was significantly higher than nighttime catchability for most species during autumn and for mature male Spiny Dogfish, shortfin squid, and longfin squid during spring in the NES LME. For most stages and species examined, breakpoint analyses identified significant increases in CPUE in the morning, peak CPUE during the day, and significant declines in CPUE in the late afternoon. Seasonal probabilities of daytime catch were largely driven by solar zenith angle for most species, with stronger trends identified during autumn. Unadjusted CPUE estimates appear to overestimate absolute abundance, with adjustments resulting in reductions in absolute abundance ranging from 41% for Spiny Dogfish to 91% for shortfin and longfin squids. These findings have important implications for Spiny Dogfish regarding estimates of population consumption of key pelagic prey species and their ecological footprint within the NES LME
Relative mobility determines the efficacy of MPAs in a two species mixed fishery with conflicting management objectives
Marine Protected Areas (MPAs) have been used to protect species in need of conservation and as a fisheries management tool. It has been suggested MPAs can benefit mobile stocks by protecting spawning grounds whilst also allowing yields to be maintained as mature fish move out of the protected areas. However, the robustness of this claim in mixed species fisheries has yet to be established. We use a simulation model to explore the efficacy of spatial closures and effort regulation when other forms of fishery control (e.g., Total Allowable Catches) are absent or non-enforced as ways of addressing management objectives that are difficult to reconcile due to the contrasting life-histories of a target and a bycatch, conservation species in a two-species fishery. The mobility of each stock in such a fishery affects the benefits conferred by an MPA. The differing management objectives of the two species can be partially met by effort regulations or closures when the species exhibit similar mobility. However, a more mobile conservation species prevents both sets of aims being met by either management tool. We use simulations to explore how spatial closures and effort regulation can be used to seek compromise between stakeholders when the mobility of one stock prevents conflicting management objectives to be fully met. Our results demonstrate that stock mobility is a key factor in considering whether an MPA can meet conflicting aims in a multispecies fishery compromised of stocks with differing life histories and mobilities
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