Gulf Menhaden Research Articles

Assessing the utility of computer vision for age determination of Gulf Menhaden

AbstractObjectiveIn this work, we assess the potential of computer vision techniques for age estimation of Gulf Menhaden Brevoortia patronus scales. Scales are the primary structure used for the age determination of Gulf Menhaden, and the ageing process can be labor intensive. Gulf Menhaden is the second‐largest fishery by weight in the United States, with average annual landings from 2018 to 2022 of 449,540 metric tons, and is assessed with age‐structured models that require information about the age structure of the catch and the stock.MethodsWe used convolutional neural networks and deep neural networks to classify the age from images of Gulf Menhaden scales from three different sets of images of scales. The first set of data consists of images of scales from fish at ages 0 and 1 year. The second set of data consists of images of scales from fish at ages 0–4 years. The last set of data consists of images of scales from fish of ages 0, 1, and 2 years and includes only images of scales for which there is agreement by readers of age estimates derived from analyzing sagittal otoliths and scales from the same individual.ResultThe classification of ages was best when using a convolutional neural network model on the first data set. The poorest classification was for the model using deep neural networks with the second data set.ConclusionAlthough we show that computer vision has promise for age determination from fish scale samples, our results indicate that considerable work must be done for wide adoption of the approach. With the continuous enhancements of computer vision models, improvements in the quality of scale images, and the accumulation of larger sets of scale images that can be used to train machine learning models, we believe that using computer vision can serve to reduce processing time and increase the accuracy of age estimates.

Combining biotracer and stomach contents analysis to understand trophic dynamics in the northern Gulf of Mexico

The northern Gulf of Mexico (nGOM) is a taxonomically rich ecosystem. Previous work based on a meta-analysis of stomach contents data has shown the trophic connectivity of predators and prey to be substantial. However, the trophic dynamics of many economically and ecologically important species are still not well understood. Sportfish, such as Spotted Seatrout (Cynoscion nebulosus), Red Drum (Sciaenops ocellatus), and Southern Flounder (Paralichthys lethostigma), support recreational fisheries throughout the region. Gulf Menhaden (Brevoortia patronus), a high biomass forage fish with the region's largest commercial fishery, is considered an important forage species. In this study, we use information from meta-analysis of stomach contents and stable isotope analysis to investigate the importance of prey taxa, including Gulf Menhaden, for nGOM nearshore predators. Stomach contents and stable isotope analyses are generally evaluated independently, with stomach contents used to directly identify trophic interactions, while stable isotopes of carbon (δ13C) and nitrogen (δ15N) provide insight into a consumer's long-term feeding habits. We used a multispecies trophic model, EcoDiet, developed by Hernvann et al. (2022), that integrates information of both stomach contents and stable isotopes into a single framework to estimate trophic link probabilities and diet proportions. Data in the model include n = 41 predators, n = 173 prey, and n = 497 unique predator and prey interactions. The results indicate that nGOM nearshore predators are generalists using the diverse prey base, and in concordance with previous findings, there is no single Menhaden-dependent predator. Our findings better quantify the trophic interactions of the highly diverse nGOM region and have important implications regarding future ecosystem modeling and management considerations for the Gulf Menhaden stock.

Physiological, temporal, and environmental determinants of dry energy densities of low trophic-level fishes in the Gulf of Mexico

Low trophic-level fishes provide a link to higher trophic-level animals, including birds, mammals, and economically valuable fishes. Despite their role, the dry energy density (DED) of these fishes and its variability have not been described in the northern Gulf of Mexico (nGOM). To address this, we describe species-specific DED for four fish species in the nGOM: Atlantic Croaker (Micropogonias undulatus), Gulf Menhaden (Brevoortia patronus), White Trout (Cynoscion arenarius), and Bay Anchovy (Anchoa mitchilli). We investigated the impacts of body length, life stage (juvenile and adult), month of collection, and river discharge from the Mississippi River to determine the response of DED for Atlantic Croaker and Gulf Menhaden. Using bomb calorimetry, we found that the DED of Atlantic Croaker ranged from 3021 to 6445 calories/g (mean = 4524 ± 646 calories/g SD, n = 129), Gulf Menhaden DED ranged from 2578 to 6821 calories/g (mean = 5069 calories/g ± 794 SD, n = 193), White Trout DED ranged from 3118 to 4581 calories/g (mean = 4120 calories/g ± 358 SD, n = 30), and Bay Anchovy DED ranged from 3925 to 4387 calories/g (mean = 4261 ± 126 calories/g SD, n = 74). The mean DED of Gulf Menhaden and Atlantic Croaker varied and was at a minimum during the fall. The DED of Gulf Menhaden and Atlantic Croaker were linearly, positively, and significantly (α = 0.05) related to fork length (R2 = 0.23 and R2 = 0.32, respectively). The flow rate of the Mississippi River was not a significant predictor of the DED of juvenile or adult Gulf Menhaden but was a significant predictor of the DED of adult Atlantic Croaker (p < 0.001, R2 = 0.04). The species-specific energy density values and the variations due to the month of collection, environmental conditions, and physiological variation will serve to inform ecosystem models.

Identifying trade-offs and reference points in support of ecosystem approaches to managing Gulf of Mexico menhaden

Gulf menhaden (Brevoortia patronus) support the largest fishery by yield in the Gulf of Mexico (GoM) and are a key forage species for many marine predators. While menhaden stock assessments indicated that overfishing was not likely to have occurred in the past, concerns have been raised regarding the possible effects of menhaden fishing on their predators. In this study, we used a US Gulfwide Ecopath with Ecosim (EwE) model to explore the predicted effects of increased menhaden harvest on the GoM ecosystem and focused our analyses on Gulf menhaden predators. Key menhaden predators identified included king mackerel (Scomberomorus cavalla), Spanish mackerel (Scomberomorus maculatus), sea trout (Cynoscion spp.), red drum (Sciaenops ocellatus), and pelagic coastal piscivores [e.g., bluefish (Pomatomus saltatrix)]. As expected, these predators exhibited reduced biomass in response to increased Gulf menhaden harvest, with a predicted 11% decrease in predator biomass at simulated fishing levels near historical highs. Our results indicate strong relationships between the effects of menhaden fishing and the predator fishing mortality for king mackerel and intermediate relationships for Spanish mackerel, blacktip shark (Carcharhinus limbatus), red drum, large coastal sharks, and pelagic coastal piscivores. Biomass of predator groups such as demersal coastal invertebrate feeders [e.g., drums and croakers (Sciaenidae)] are more affected by menhaden harvest (through trophodynamics interactions and bycatch removal) compared to the isolated effect of their fishing mortality. For almost all the groups examined in the trade-off analysis, with the exception of sea trout, current biomass (2016) was higher than their target biomass representing 75% of their biomass at maximum sustainable yield. In comparison to the time series of fishing mortality rates estimated by the most recent Gulf menhaden stock assessment, the mean ecological reference point (ERP) of 0.862 was exceeded in all but 1 year from 1977 to 2007; however, neither the target nor threshold upper ERP value has been exceeded since 2008. The observed Gulf menhaden landings from 2003 to the present were generally within the range of the projected equilibrium landings (i.e., within confidence intervals) at both the ERP target and threshold values except for three recent years.

Variation in larval Gulf Menhaden diet, growth and condition during an atypical winter freshwater-discharge event in the northern Gulf of Mexico

In January 2016, historic levels of rainfall in the upper Mississippi River Basin prompted the earliest opening of the Bonnet Carré Spillway, a water control structure on the Mississippi River that diverts flood-stage river water through an alternate pathway (Lake Pontchartrain) into the northern Gulf of Mexico. This unprecedented winter opening of the spillway coincided with the spawning season and larval ingress period for Gulf Menhaden, a forage fish species that supports the largest commercial fishery in the region. Oceanographic observations and plankton samples were collected in the Mississippi Bight region shortly after the Bonnet Carré Spillway winter opening to examine the impacts on larval Gulf Menhaden feeding, growth and condition. Three distinct water masses were identified based on temperature, salinity, and particle scattering (proxy for turbidity) characteristics. Larval Gulf Menhaden with the highest growth rates and body condition were collected in a water mass defined by relatively high temperature and salinity and relatively low turbidity and zooplankton (prey) abundance. In contrast, larvae with the slowest growth rates and poor body condition were collected in a water mass with the highest zooplankton abundance, but also highest turbidity and lowest temperature and salinity. This water mass was nearest the diversion outflow and most impacted by the spillway opening. Our results indicate that the anomalous freshwater discharge event resulted in hydrographic conditions that diminished otherwise favorable larval fish foraging habitat with abundant zooplankton prey. These findings suggest that the recent trend of Bonnet Carré Spillway openings may result in negative consequences for larval fish survival and subsequent fishery recruitment.

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. fig. 15

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. fig. 15

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus)

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus)

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 16-17

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 16-17

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. table 2

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. table 2

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 7-14

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 7-14

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 1-6

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. figs. 1-6

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. fig. 18

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. fig. 18

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. table 1

Comparison of ages determined by using an Eberbach projector and a microscope to read scales from Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (B. patronus): suppl. table 1

Evidence for Ecosystem-Level Trophic Cascade Effects Involving Gulf Menhaden (Brevoortia patronus) Triggered by the Deepwater Horizon Blowout

Unprecedented recruitment of Gulf menhaden (Brevoortia patronus) followed the 2010 Deepwater Horizon blowout (DWH). The foregone consumption of Gulf menhaden, after their many predator species were killed by oiling, increased competition among menhaden for food, resulting in poor physiological conditions and low lipid content during 2011 and 2012. Menhaden sampled for length and weight measurements, beginning in 2011, exhibited the poorest condition around Barataria Bay, west of the Mississippi River, where recruitment of the 2010 year class was highest. Trophodynamic comparisons indicate that ~20% of net primary production flowed through Gulf menhaden prior to the DWH, increasing to ~38% in 2011 and ~27% in 2012, confirming the dominant role of Gulf menhaden in their food web. Hyperabundant Gulf menhaden likely suppressed populations of their zooplankton prey, suggesting a trophic cascade triggered by increased menhaden recruitment. Additionally, low-lipid menhaden likely became “junk food” for predators, further propagating adverse effects. We posit that food web analyses based on inappropriate spatial scales for dominant species, or solely on biomass, provide insufficient indication of the ecosystem consequences of oiling injury. Including such cascading and associated indirect effects in damage assessment models will enhance the ability to anticipate and estimate ecosystem damage from, and provide recovery guidance for, major oil spills.

A Synthesis of Deepwater Horizon Impacts on Coastal and Nearshore Living Marine Resources

The 2010 Deepwater Horizon (DWH) oil blowout in the Gulf of Mexico began on April 20, originating in the deep sea 66 km off the Louisiana coast. By early June, DWH oil had spread to coastal Louisiana, Mississippi, Alabama and western Florida. An estimated 2,113 km of shoreline were oiled, making DWH the largest marine oil spill in global history by length of affected shoreline. Additionally, a series of oil spill response measures were deployed, including diversions of Mississippi River discharge to forestall oil coming ashore, and the establishment of large-scale fishery closures, with both affecting coastal resources to varying degrees. Here, we review published studies and describe additional analyses evaluating long-term impacts of DWH on coastal/nearshore biological resources. We assembled time-series data collected by state, federal and academic partners on population abundance and environmental conditions to evaluate species and community change. Our study focused on plankton, invertebrates, fishes and dolphins, and 13 “key species” were selected to conduct semi-quantitative vulnerability-resilience (V-R) analyses. At one extreme, early life stages of Gulf Menhaden (Brevoortia patronus) were not affected due to seasonal spawning and larval development preceding the spill. In contrast, demographically independent populations of the common Bottlenose Dolphin, (Tursiops truncatus) suffered a variety of severe and ongoing health effects owing to oil exposure. Virtually all of the heavily oiled salt marsh habitat was in Louisiana, with the majority occurring in Barataria Bay. Multispecies trawl survey abundances declined post-DWH throughout eastern coastal Louisiana but remained stable elsewhere. A regime shift in composition of Barataria Bay trawl survey catches occurred during and following the spill, the persistence of which was associated with long-term reductions in average salinity and increases in water clarity. In some cases, fishery closures were associated with measurable but ephemeral increases in abundance of some targeted and bycatch species. Freshwater flooding of marshes was ineffective in preventing coastal oiling and severely affected benthic euryhaline resources including Eastern Oyster (Crassostrea virginica) and Marsh Periwinkle (Littoraria irrorata). The flooding response measure experiment also indicates the directionality of impacts that further planned water diversions may have on ecological communities of lower Mississippi River basins.

A Simulation‐Based Evaluation of Commercial Port Sampling Programs for the Gulf and Atlantic Menhaden Fisheries

AbstractBiological data that are collected in commercial port sampling programs are a critical component of the assessment and management of Gulf Menhaden Brevoortia patronus and Atlantic Menhaden Brevoortia tyrannus. The menhaden port sampling program represents one of the longest continuous commercial sampling efforts in the United States; however, this sampling program has not been evaluated recently to determine whether the program adequately characterizes the size and age structure of the catch despite significant changes in the spatial extent and magnitude of the fisheries in the last three decades. We conducted a simulation study to evaluate current menhaden fishery sampling targets and to examine the relative performance of a suite of alternative targets. To simulate data collection, we conducted a bootstrap analysis of the observed port sampling data. These observations were resampled with replacement across a range of current and alternative combinations of number of trips and fish sampled per trip. At the current target for sampling intensity and allocation, the mean sample weight and proportions at age for ages 2 and 3 are well characterized in both the Gulf and Atlantic menhaden fisheries. The proportions of age‐1 fish in the catch differed by stock and region, with samples from the northern Atlantic regions displaying the greatest uncertainty overall. The proportions of age‐4 and older fish were poorly characterized in both fisheries, which is likely due to their rarity in the population (Gulf) and lack of spatial overlap between the fishery and the stratified distribution of menhaden by age along the coast (Atlantic). Our results indicate that reducing the number of fish that is sampled per trip from the current target of 10 to as few as four would have a minimal effect on estimates of mean size and proportions at age in the catch. Increasing the number of sampled trips will not greatly improve the characterization of catch size or age composition.

Macroscale drivers of Atlantic and Gulf Menhaden growth

AbstractThe identification of anthropogenic and environmental drivers on length‐at‐age of fish stocks is important to understanding ecosystem dynamics and harvest intensity. We evaluated coastwide annual growth of n = 187,115 Atlantic Menhaden (Brevoortia tyrannus) and n = 299,185 Gulf Menhaden (B. patronus), using samples collected from the North, Mid‐, and South Atlantic from 1961 to 2016 and across the Gulf of Mexico from 1977 to 2016. Using hierarchical models of age 1 growth and age 2 growth, we evaluated a suite of candidate predictors including fishery landings, easterly (U) and northerly (V) wind velocity, river discharge, juvenile abundance, and the Atlantic Multi‐decadal Oscillation (AMO). We found age 2 growth rates were smaller than age 1 growth rates for both species and that Atlantic Menhaden growth rates were 3–4 times greater than Gulf Menhaden. Age 1 growth rate of Atlantic Menhaden was positively affected by landings lagged by one year, indicating a density‐dependent mechanism. In addition, AMO (negative effect), and wind U (positive effect) and wind V (negative effect) in the North Atlantic region were significant factors influencing coastwide age 1 Menhaden growth. Wind V (negative effect) and AMO (positive effect) influenced age 1 Gulf Menhaden growth. No environmental factors were found to have an effect on age 2 Atlantic Menhaden growth, and AMO was the only significant predictor (weak negative effect) of age 2 Gulf Menhaden growth. Fishing pressure was the primary influence on age 1 Atlantic Menhaden growth, whereas age 1 Gulf Menhaden growth was primarily influenced by environmental conditions.

Diet of the Blacktip Shark (Carcharhinus limbatus) in the Northwestern Gulf of Mexico

The stomach contents of 90 Blacktip Shark (Carcharhinus limbatus) specimens caught in the northwestern Gulf of Mexico (GOM) were examined. Stomach contents were identified to the lowest possible taxon, and quantified using percent weight, percent number, percent frequency of occurrence, and percent index of relative importance (IRI). Teleosts were the dominant prey group (98.95% IRI), although most were unidentified (61.70% IRI). Of identified teleost species, Atlantic Croaker (Micropogonias undulatus) (28.43% IRI), and Gulf Menhaden (Brevoortia patronus) (2.31% IRI) were the most important. Crustaceans (0.65% IRI), mollusks (0.46% IRI), and elasmobranchs (0.03% IRI) formed a minor component of the diet. Suspected shrimp fishery discards were found in 11% of stomachs, highlighting the potential importance of this food source for the Blacktip Shark. Diet composition did not differ between male and female sharks, but did between juveniles and adults. Juvenile shark diets had greater proportions of unidentified teleost, Clupeidae and Penaeidae, while adult diets had greater proportions of Sciaenidae, Ariidae and cephalopods. Our results were similar, although not identical to, other studies of Blacktip Shark diets in the northwestern GOM. Of note is finding of the mantis shrimp Squilla empusa, a species previously unreported in Blacktip Shark stomach contents. This new finding, the high importance of unidentified teleosts, and the lack of asymptote in the prey accumulation curve emphasize the need for further study of the Blacktip Shark diet in the northwestern GOM.

Freshwater Predators on the Edge: Assessing the Temporal and Spatial Variation in Diet of Largemouth Bass in Mobile Bay Estuary, Alabama, USA

AbstractEstuaries present a set of unique challenges for freshwater fish. In addition to basic physiological challenges, the influx of salinity can affect prey availability and can influence resource consumption. Diets of coastal Largemouth Bass Micropterus salmoides were surveyed from three sites in the Mobile Bay estuary, Alabama, USA, from April 2011 to April 2015. A large proportion of Largemouth Bass consumed blue crabs Callinectes sapidus (proportion occurrence [PO] = 0.38) and mud crabs Panopeus spp. (PO = 0.24). Largemouth Bass also consumed grass shrimp Palaemonetes spp. (PO = 0.16), Gulf Menhaden Brevoortia patronus (PO = 0.14), and mysid shrimp Mysidopsis spp. (PO = 0.12). Prey diversity was greater at the lower estuary site (Fowl River) than at the sites in the upper estuary (Bay Minette and D'Olive Bay). A principal components analysis based on the biomass diet data revealed that invertebrates were the most important prey resource for coastal Largemouth Bass, with finfishes playing a secondary role. Seasonal inputs of estuarine fish species, such as Gulf Menhaden, represented an important prey resource in the diets of Largemouth Bass during both spring and summer.

Construction and evaluation of a robust trophic network model for the northern Gulf of Mexico ecosystem

A critical issue in understanding trophic connectivity in ecological systems is the lack in quality and quantity of information about feeding habits. In this work, we present a method for integrating a diversity of feeding habits data from published studies to evaluate the impact on indices that describe characteristics of individual taxa and their connectivity. We focus our study on feeding habits of the fishes of the northern Gulf of Mexico and seek to understand the importance of the forage fish Gulf Menhaden (Brevoortia patronus) in predator diets. We created a database of diet studies from the northern Gulf of Mexico that included six diet metrics: frequency of occurrence, wet weight, dry weight, number, volume, index of relative importance, and index of caloric importance. We then used this information to construct a set of traditional networks (all prey and predators were from a single taxonomic level and trophic connections were parameterized with a single diet metric). We also constructed a “robust” network where all taxa were identified to the lowest taxonomic level and trophic connections were parameterized using a resampling approach that included all available information. Linear regression and resampling methods were used to convert data reported in other diet metrics into the frequency of occurrence diet metric. For both traditional and robust networks, we used network indices to describe topological properties. With the robust network, we conducted removal simulations where the forage fish species Gulf Menhaden, and associated Clupeidae representatives, were removed from the network and the feeding effort of the predators was reallocated among their other prey items. We found that network and node-specific indices were sensitive to the choice of taxonomy and diet metric level. In the robust network, predator species with the greatest number of identified prey had the lowest precision in their connections and prey from the Arthropoda phyla had the lowest precision for connections. From the removal and reallocation simulations, we found that Actinopterygii and Arthropoda were the most impacted prey taxa with 1.2% to 4.3% increase in predation and approximately 23 taxa would receive 50% of the reallocated predation. Overall, the resampling methods we present provide a potential means for combining disparate diet data and enables a comprehensive understanding of trophic interactions within an ecosystem.