Sort by
Good practices, trade-offs, and precautions for model diagnostics in integrated stock assessments

Carvalho et al. (2021) provided a “cookbook” for implementing contemporary model diagnostics, which included convergence checks, examinations of fits to data, retrospective and hindcasting analyses, likelihood profiling, and model-free validation. However, it remains unclear whether these widely-used diagnostics exhibit consistent behavior in the presence of model misspecification, and whether there are trade-offs in diagnostic performance that the assessment community should consider. This illustrative study uses a statistical catch-at-age simulation framework to compare diagnostic performance across a spectrum of correctly specified and mis-specified assessment models that incorporate compositional, survey, and catch data. Results are used to contextualize how reliably common diagnostic tests perform given the degree and nature of known model issues, including parameter and model process misspecification, and combinations thereof, and trade-offs among model fits, prediction skill, and retrospective bias that analysts must consider as they evaluate diagnostic performance. A surprising number of mis-specified models were able to pass certain diagnostic tests, although there was a trend of more frequent failure with increased mis-specification for most diagnostic tests. Nearly all models that failed multiple tests were mis-specified, indicating the value of examining multiple diagnostics during model evaluation. Diagnostic performance was best (most sensitive) when recruitment variability was low and historical exploitation rates were high, likely due to the induction of better contrast in the data, particularly indices of abundance, under this scenario. These results suggest caution when using standalone diagnostic results as the basis for selecting a “best” assessment model, a set of models to include within an ensemble, or to inform model weighting. The discussion advises stock assessors to consider the interplay across multiple dynamics. Future work should evaluate how the resolution of the production function, quality and quantity of data time series, and exploitation history can influence diagnostic performance.

Just Published
Relevant
Spatiotemporal dynamics and habitat use of red snapper (Lutjanus campechanus) on the southeastern United States Atlantic continental shelf

Red snapper (Lutjanus campechanus) is an iconic marine fish species along the southeast United States coast. Despite its ecological and economic importance, surprisingly little is known about red snapper biology and habitat use on the southeast United States Atlantic continental shelf (SEUS). We used data from a long-term baited trap and video survey (2011–2022), as well as from remotely operated vehicle (ROV) sampling (2021–2023), to quantify temporal changes in relative abundance, patterns of spatial distribution, and habitat use of red snapper in the SEUS. Using generalized additive models, we showed that red snapper increased in relative abundance from 2011 to 2022 by ∼ 1000 % in both trap and video samples. Red snapper relative abundance was highest in mid-shelf waters off the east coast of Florida, Georgia, and, to a lesser extent, off the Outer Banks of North Carolina; red snapper were less common off southern North Carolina and South Carolina. Highest relative abundance of red snapper occurred in locations with a moderate amount of natural structured habitat and high seafloor complexity and were never observed at randomly selected ROV stations (n = 197) lacking structured habitat. These results increase our understanding of the spatial and temporal distribution of red snapper, improve our knowledge of red snapper habitat use, and can be used when scaling local density estimates to the entire SEUS.

Open Access Just Published
Relevant
Evaluating the contributions and economic costs for Walleye fry and fingerling stocking in a large midwestern reservoir

Stocking is a common management practice to maintain Walleye populations where natural recruitment is low or to introduce and sustain Walleye populations outside of their native range. Walleye can be stocked at multiple lengths (e.g., fry and fingerling) and different sizes of stocked Walleye may contribute differently to Walleye year class strength, depending on the system into which they are stocked. The cost associated with stocking also varies by product. Therefore, it is important to determine the contributions from different stocked products within a region or for an individual waterbody. The objectives of our research were to 1) compare the relative contribution of and total length and body condition at the time of capture at age-0 between stocked Walleye fry and fingerlings and naturally produced individuals; and 2) estimate and compare the economic costs of Walleye fry and fingerling production relative to their contribution to the age-0 catch in Lake McConaughy during 2022 and 2023.We collected 178 and 263 age-0 Walleyes from Lake McConaughy during the summer and fall of 2022 and 2023, respectively. Fingerling-stocked Walleye contributed 2.12 times in 2022 and 2.92 times more in 2023 than fry-stocked Walleye. Production cost estimates revealed that fry cost 1.08 and 1.35 times greater than fingerlings per stocking unit in 2022 and 2023, thus fingerlings were deemed the most cost-effective product in this study. Walleye stocked as fry were significantly longer at the time of collection in 2022 and were in significantly better condition in both years compared to fingerling stocked Walleye. Our results provide valuable insights for fisheries managers by offering a case study example as well as offering a practical approach to guide effective management decisions on which stocked product is most appropriate for other systems. Overall, this research enhances the existing literature on Walleye stocking in large reservoir systems, offering practical and useful information for effective management decisions.

Just Published
Relevant
Geospatial and environmental drivers of genetic divergence in the Indo-West Pacific spiny lobster Panulirus ornatus

The tropical ornate spiny lobster, Panulirus ornatus, is distributed widely across the Indo-West Pacific and is a highly valued seafood species. The fine-scale genetic structure of this species was examined using 13 microsatellite loci from 298 lobsters collected from 17 locations from Tanzania in the west to New Caledonia in the east and compared with mitochondrial DNA (mtDNA) and genomic (SNP) from previous studies. Significant overall genetic differentiation was observed in the microsatellite data (F’ST = 0.051, P < 0.001), but these geographic patterns differed somewhat from those seen previously in mtDNA and SNP data. For both nuclear DNA (nDNA) and mtDNA there was significant genetic divergence and reduced diversity in lobsters from Western Australia and New Caledonia, likely due to genetic bottlenecks. However, the previously identified strong divergence of lobsters from the West Indian Ocean was only minimally supported in the microsatellite data, suggesting some recent gene flow across this region had eroded past divergence in this lineage. Geographic, environmental and ocean current variables were used to detect those factors associated with genetic divergence at both mtDNA and nDNA loci. Population divergences were only partially explained by geography and were not strongly related to ocean currents. Instead, there were significant associations with ocean vorticity, convergence and sea surface temperature. These implicate strong eddy systems, characterised by high levels of convergence and/or vorticity, in constraining larval dispersal. Overall, these findings help to identify the processes driving the genetic structure of P. ornatus populations and the results have considerable implications for the management of wild fisheries for this species.

Just Published
Relevant
Short-term discard survival and catch-related trauma in European plaice (Pleuronectes platessa) caught in the Baltic Sea by Danish seine during summer

Danish seine is an active fishing gear targeting demersal species, such as European plaice (Pleuronectes platessa, hencefort referred as plaice), a commercially important fish species in the North Sea, Skagerrak, Kattegat, and Baltic Sea. Danish seining is a relevant fishery in relation to exemption from the European Union landing obligation. Trials were conducted from a commercial fishing vessel during the summer with high air temperatures and sea salinity and marked salinity and temperature gradients (pycnocline). Video equipment was used to observe fish entering the seine. Captured fish were individually tagged and housed in livewells for ten days to observe short-term survival. Reflex impairments and external injuries were assessed after capture and at the end of the observation periods using reflex action mortality predictor (RAMP) and catch-damage index (CDI) methodologies. We found that plaice entered the seine late in the towing process and that 87 % of the assessed fish survived, after 10 days of observation. There was a significant difference in short-term survival curves for fish that had been subjected to more than 30 min of on-deck during the catch-sorting process relative to those that had remained on deck for 30 min or less. The association between the time on deck and RAMP scores after capture was also significant. External injuries were primarily minor bruises, fin fraying, and net marks and changed little from after capturing to the end of the observation period.

Just Published
Relevant
The economic benefit of spearfishing as an impure public good: A case study of invasive Lionfish in Florida

Lionfish (Pterois miles and P. volitans) is a highly invasive species originally from the South Pacific and Indian Oceans. As an effort to control its exponentially growing population, the Florida Fish and Wildlife Conservation Commission has launched a program called “Lionfish Challenge” to promote harvesting of lionfish from Florida waters. The program provides anglers with a unique recreational opportunity because they would need to dive and spearfish to harvest lionfish. Furthermore, participants in the program not only gain utility from spearfishing as a private good but also as a public good, knowing that they are contributing to the ecosystem in Florida waters. This paper contributes to the literature by measuring the economic benefit for participants from spearfishing as an impure public good. Using data provided by the Florida Fish and Wildlife Conservation Commission, a travel cost method was applied to model the demand for lionfish fishing trips. Data included information about counties where lionfish were harvested at the trip-level, but only if participants took a trip and harvested lionfish. Therefore, those who are good at catching lionfish had a higher probability of being included in the data. To account for potential sample selection bias, a probability weight was applied, using the average number of lionfish harvested as a proxy. Results indicate that the per-trip consumer surplus per participant was between $965.89 and $1,597.36, depending on model specifications, with the preferred specification indicating a mean CS of $1,117.72 per trip. The seasonal consumer surplus per participant was indicated to be between $4,550.45 and $3487.91, again, depending on model specification.

Just Published
Relevant
Larval ontogeny enhances resilience to a patchy planktonic food supply in the American lobster (Homarus americanus)

The American lobster (Homarus americanus) plays an integral role in the coastal Northwest Atlantic as a benthic consumer and the target of the most valuable single-species fishery in North America. In the past decade, benthic recruitment of juvenile lobster has declined, even as egg production has increased, suggesting heightening levels of larval mortality. Recent correlative studies in the Gulf of Maine further suggest early-stage larval survival may be related to the supply and composition of planktonic foods. Despite these correlative studies and the economic importance of the species, relatively little is known about how larval lobster interacts with its prey in the pelagic environment. During these early developmental stages, lobster larvae undergo significant morphological changes which influence their ability to capture and handle prey. This study used a combination of laboratory-based feeding experiments and video recordings to examine changes in feeding behavior and ingestion rates between larval stages. Calculated Ivlev-type functional response curves were used to evaluate how larval ingestion rates vary with prey density and by larval stage on a suite of prey species. We observed dramatic stage-to-stage improvements in the capacity to pursue, capture, handle, and ingest specific prey, especially after the metamorphosis to the postlarval stage. The results highlight the vulnerability of the early life stages to low food densities. They also elucidate differences in the ability of specific prey taxa to evade predation by larval lobster. Quantifying the interactions between larval lobsters and their prey enhances our understanding of how this economically important species interacts with the pelagic food web, which fraction of available zooplankton represent viable food sources, and how lobster larvae may be impacted by altered prey availability associated with climate change.

Relevant