Gerard DiNardo

Length-Based Assessment of Coral Reef Fish Populations in the Main and Northwestern Hawaiian Islands

The coral reef fish community of Hawaii is composed of hundreds of species, supports a multimillion dollar fishing and tourism industry, and is of great cultural importance to the local population. However, a major stock assessment of Hawaiian coral reef fish populations has not yet been conducted. Here we used the robust indicator variable “average length in the exploited phase of the population (L¯)”, estimated from size composition data from commercial fisheries trip reports and fishery-independent diver surveys, to evaluate exploitation rates for 19 Hawaiian reef fishes. By and large, the average lengths obtained from diver surveys agreed well with those from commercial data. We used the estimated exploitation rates coupled with life history parameters synthesized from the literature to parameterize a numerical population model and generate stock sustainability metrics such as spawning potential ratios (SPR). We found good agreement between predicted average lengths in an unfished population (from our population model) and those observed from diver surveys in the largely unexploited Northwestern Hawaiian Islands. Of 19 exploited reef fish species assessed in the main Hawaiian Islands, 9 had SPRs close to or below the 30% overfishing threshold. In general, longer-lived species such as surgeonfishes, the redlip parrotfish (Scarus rubroviolaceus), and the gray snapper (Aprion virescens) had the lowest SPRs, while short-lived species such as goatfishes and jacks, as well as two invasive species (Lutjanus kasmira and Cephalopholis argus), had SPRs above the 30% threshold.

Habitat suitability analysis and identification of potential fishing grounds for swordfish, Xiphias gladius, in the South Atlantic Ocean

Swordfish, Xiphias gladius, is a highly migratory species of important commercial value and widely distributed in three oceans. Recently, the South Atlantic swordfish captured as by-catch in longline fisheries targeting tunas has contributed greatly to the overall Atlantic swordfishs landing. In this study, we have developed a habitat suitability index (HSI) model to examine the relationships between their spatio-temporal distribution and environmental factors and to identify potential fishing grounds for the swordfish in the South Atlantic Ocean using the Taiwanese distant-water longline fishery data and remote-sensing oceanographic data for 1998–2007. All the environmental factors considered – sea surface temperature (SST), mixed layer depth (MLD), sea surface height anomaly (SSHA), chlorophyll-a concentration (CHA) and ocean bathymetry (BAH) – were highly significant with most of the catch-per-unit-effort (CPUE) variation explained by SST. The most optimum habitat (i.e. hotspot) was found in the areas with SSTs of 27–28°C, SSHAs of −0.05 to 0.05 m, CHAs of 0.1–0.2 mg m−3 and BAHs of −4000 to −4500 m. The arithmetic mean model with five environmental variables was found to be the most appropriate according to the information theory based on the evaluation of different empirical HSI models in combination with different environmental factors. The bimonthly geographic information system maps of the predicted HSI values were cross-validated by the observed CPUE, suggesting that the model can be used as a tool for reliable prediction of potential fishing grounds. Because the distribution and relative abundance of swordfish are sufficiently heterogeneous in space and time, the output of this study could provide a scientific basis for time–area closures based management of this species.

Sex-structured population dynamics of blue marlin Makaira nigricans in the Pacific Ocean

The population dynamics of the blue marlin Makaira nigricans stock in the Pacific Ocean were estimated for 1971–2011 using a fully integrated length-based, age-, and sex-structured model. Fishery-specific catch, size composition, and catch-per-unit of effort were used in the modeling as likelihood components. Estimated dynamics were consistent with a stock that is fully exploited and stable over the last several years. No significant trends in recruitment were noted; however, female blue marlin were estimated to make up a majority of the catch, and historical exploitation has disproportionately changed the age structure of females relative to males. This result is due to differences in assumed life history and estimated selectivity. Changes to important life history parameters that are responsible for the productivity of the stock would potentially change the interpretation of current stock status.

Incorporating habitat preference into the stock assessment and management of blue marlin (Makaira nigricans) in the Pacific Ocean

Stock assessments that include a spatial component or relate population dynamics to environmental conditions can be considered one way of implementing an ecosystem approach to fisheries. A spatially-structured population dynamics model that takes account of habitat preference is developed and then applied to Pacific blue marlin (Makaira nigricans), as they prefer certain habitats and migrate seasonally. The model is fitted to fishery catch-rate and size data, along with information on the relative density of the population over space derived from a habitat preference model fitted to oceanographic and biological variables. Results show that blue marlin are more abundant in tropical waters, and females account for most of the biomass. Assessments that allow for environmental factors, movement dynamics and sexual dimorphism indicate that this population is in an over-exploited state, with current spawning stock biomass below the level corresponding to maximum sustainable yield (SMSY) and current fishing mortality exceeding that needed to achieve MSY (FMSY). A risk analysis based on samples from a Bayesian posterior distribution suggests that the population will remain above SMSY after 20 years if exploitation rates are below the level corresponding to FMSY.

Regional-scale surface temperature variability allows prediction of Pacific bluefin tuna recruitment

Regional-scale surface temperature variability allows prediction of Pacific bluefin tuna recruitment Barbara A. Muhling*, Desiree Tommasi, Seiji Ohshimo, Michael A. Alexander, and Gerard DiNardo Cooperative Institute for Marine Ecosystems and Climate (CIMEC), University of California Santa Cruz, La Jolla, CA 92037, USA NOAA National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA 92037, USA National Research Institute of Far Seas Fisheries, Japan Fisheries Research and Education Agency, 5-7-1 Orido Shimizu-ku, Shizuoka 424-8633, Japan NOAA Earth System Research Laboratory, Boulder, CO 80305, USA *Corresponding author: tel: þ1 858 546 7197; fax: þ1 858 546 7003; e-mail: barbara.muhling@noaa.gov

Factors influencing the distribution of Kona crabs Ranina ranina (Brachyura: Raninidae) catch rates in the Main Hawaiian Islands

A generalized linear model and commercial catch report data were used to describe spatial and temporal patterns in Kona crab, Ranina ranina Linnaeus, 1758, catch rates in the Main Hawaiian Islands. Three alternative hypotheses regarding factors influencing the temporal and spatial distribution of Kona crabs were evaluated using multi-model inference. Broad-scale island effects explain the spatial distribution of catch rates better than the finer-scale factors of depth and swell exposure. Interdecadal declines in catch rates were noted for islands with high human density, while other islands had stable or increasing catch rates. The interdecadal changes in catch rates may be explained by changes in population abundance and management-induced changes in fishing patterns in the recent period. Kona crab behaviors associated with the reproductive cycle contribute to seasonal variations in observed catch rates.

Length-based risk analysis for assessing sustainability of data-limited tropical reef fisheries

&NA; This study extended a “data‐limited” length‐based stock assessment approach to a risk analysis context. The estimation‐simulation method used length frequencies as the principal data in lieu of catch and effort. Key developments were to: (i) incorporate probabilistic mortality and growth dynamics into a numerical cohort model; (ii) employ a precautionary approach for setting sustainability reference points for fishing mortality (FREF) and stock reproductive biomass (BREF); (iii) define sustainability risks in terms of probability distributions; and, (iv) evaluate exploitation status in terms of expected length frequencies, the main “observable” population metric. This refined length‐based approach was applied to six principal exploited reef fish species in the Florida Keys region, consisting of three groupers (black grouper, red grouper, and coney), two snappers (mutton snapper and yellowtail snapper), and one wrasse (hogfish). The estimated sustainability risks for coney were low (<35%) in terms of benchmarks for fishing mortality rate and stock reproductive biomass. The other five species had estimated sustainability risks of greater than 95% for both benchmarks. The data‐limited risk analysis methodology allowed for a fairly comprehensive probabilistic evaluation of sustainability status from species and community perspectives, and also a frame of reference for exploring management options balancing sustainability risks and fishery production.