Variability of preferred environmental conditions for Atlantic bluefin tuna (Thunnus thynnus) larvae in the Gulf of Mexico during 1993–2011

The Gulf of Mexico (GOM) is the primary spawning ground for western Atlantic bluefin tuna (Thunnus thynnus). In this work, information reported by previous studies about the preferred environmental conditions for the occurrence of bluefin tuna larvae in the GOM is integrated into a dimensionless index, the BFT_Index. This index is used to evaluate the spatial and temporal variability of areas with favorable environmental conditions for larvae within the GOM during 1993–2011. The main findings of this work are that: (i) the proposed index successfully captures the spatial and temporal variability in the in situ occurrence of bluefin tuna larvae; (ii) areas with favorable environmental conditions for larvae in the GOM exhibit year‐to‐year spatial and temporal variability linked with mesoscale ocean features and sea surface temperature; and (iii) comparison of the BFT_Index‐derived variability with recruitment of age‐0 fish estimated from recent stock assessment indicates that changes in environmental conditions may drive a relevant component (~58%) of the recruitment variability. The comparison with the recruitment dataset further revealed the existence of key regions linked with recruitment in the central/northern GOM, and that the Loop Current may function as a trap for larvae, possibly leading to low survival rates. Above (below) average conditions for occurrence of larvae in the GOM during spring were observed in 2000, 2001, 2002, 2006–2008, and 2011 (1994, 1996, 1998, 1999, 2003 and 2010). Results reported here have potential applications to assessment of bluefin tuna.     

Bluefin tuna (Thunnus thynnus) distribution in relation to sea surface temperature fronts in the Gulf of Maine (1994–96)

Fishery‐linked aerial surveys for bluefin tuna (Thunnus thynnus) were conducted in the Gulf of Maine (GOM) from July through October, 1994–96. Each year, from 507 to 890 surface schools were detected and their locations examined in relation to oceanographic conditions. Correlations between bluefin tuna presence and environmental variables were explored for sea surface temperature (SST), distance to a SST front, frontal density (relative density of all SST fronts seen in a given 1 km area for 2 weeks prior to each tuna sighting), and bottom depth and slope. Mean SST associated with bluefin schools was 18.1°C (±2.8). Schools were located at a mean distance of 19.7 km (±19.6) from SST fronts, and in water masses with an average frontal density of 28.2 m km^?2 (±35.7). Mean bottom depth of detected schools was 139.0 m (±70.3), and mean bottom slope was 0.7% rise (±0.7). A binomial generalized linear model fit to these variables indicated that bluefin are seen closer to fronts than locations in which no tuna were seen. Using simple and partial Mantel tests, we investigated the spatial correlation between bluefin tuna presence and the environmental variables, controlling for spatial autocorrelation. For each day that schools were sighted, we performed 24 Mantel tests, on a combination of response and predictor variables. The spatial relationship between bluefin tuna and SST fronts was inconsistent. Our analysis identified significant spatial structure in the bluefin school locations that had no significant correlation with any of the measured environmental features, suggesting that other untested features, such as prey density, may be important predictors of bluefin distribution in the GOM.     

Environmental influences on Atlantic bluefin tuna (Thunnus thynnus) catch per unit effort in the southern Gulf of St. Lawrence

The Atlantic bluefin tuna (Thunnus thynnus) population in the western Atlantic supports substantial commercial and recreational fisheries. Despite quota establishment and management under the auspices of the International Commission for the Conservation of Atlantic Tunas, only small increases in population growth have been estimated. In contrast to other western bluefin tuna fisheries indices, contemporary estimates of catch per unit effort (CPUE) in the southern Gulf of St. Lawrence have increased rapidly and are at record highs. This area is characterized by the Cold Intermediate Layer (CIL) that is defined by waters <3°C and located at depths of 30–40 m in September. We investigated the influence of several in situ environmental variables on the bluefin tuna fishery CPUE using delta‐lognormal modelling and relatively extensive and consistent oceanographic survey data, as well as dockside monitoring and mandatory logbook data associated with the fishery. Although there is considerable spatial and temporal variation of water mass characteristics, the amount of available habitat in the southern Gulf of St. Lawrence (assuming a > 3°C thermal ambit) for bluefin tuna has been increasing. The percentage of the water column occupied by the CIL was a significant environmental variable in the standardization of CPUE estimates. There was also a negative relationship between the spatial extents of the CIL and the fishery. Properties of the CIL account for variation in the bluefin tuna CPUE and may be a factor in determining the amount of available feeding habitat for bluefin tuna in the southern Gulf of St. Lawrence.     

Comparison of the lipid profiles from wild caught eggs and unfed larvae of two scombroid fish: northern bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis> L., 1758) and Atlantic bonito (<Emphasis Type="Italic">Sarda sarda</Emphasis> Bloch, 1793)

Lipids and essential fatty acids are determinants of the reproductive process in marine fish, affecting fecundity, egg quality, hatching performance, pigmentation and larval malformation. We have analyzed and characterized the lipids of eggs and unfed larvae of two wild caught scombroid fish, the Atlantic northern bluefin tuna (Thunnus thynnus) and Atlantic bonito (Sarda sarda). Dry matter and total lipid contents, polar and neutral lipid classes and total lipid fatty acid contents were determined in the eggs of bluefin tuna and eggs and unfed larvae during the development of Atlantic bonito. Bluefin tuna eggs had slightly but significantly more dry mass than bonito eggs but very similar lipid content. However, bluefin tuna eggs presented a higher polar lipid content due to increased proportions of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). Bonito eggs and larvae showed increasing dry mass and decreasing lipid content with development. The proportion of polar lipids increased due to increased PE, PS and PI, whereas choline-containing polar lipids (phosphatidylcholine and sphingomyelin) remained relatively constant. Free cholesterol also increased, whereas the levels of other neutral lipids, especially triacylglycerol and steryl ester fractions, decreased, presumably due to utilization for energy to drive development. Bluefin tuna eggs had higher levels of n − 3 and n − 6 highly unsaturated fatty acids due to higher docosahexaenoic and arachidonic acid contents, respectively, than bonito eggs. The results are discussed in relation to the lipid and fatty acid requirements of larval scombroid fish in comparison to those of other larval marine finfish species under culture conditions.     

Inclusion of prey data improves prediction of bluefin tuna (Thunnus thynnus) distribution

We examined the distribution of Atlantic bluefin tuna ( Thunnus thynnus ) in the Gulf of Maine, Northwest Atlantic Ocean, from 17 to 23 August 1995, in relation to physical and biological parameters. Specifically, we fit a binomial GLM to the bluefin tuna presence–absence data and predictor variables that include: sea surface temperature (SST), ocean depth, distance to an SST front, time-lagged density of SST fronts, and an interpolated surface of Atlantic herring ( Clupea harengus ) density. In addition, we use simple and partial Mantel tests to examine whether bluefin tuna presence–absence data are significantly associated with these predictors, once spatial autocorrelation is accounted for. Results suggest that the distribution of bluefin tuna significantly correlated with herring density ( z  =   3.525, P  =   0.000424), and that inclusion of biological variables results in a more parsimonious model. Mantel tests results indicate that bluefin tuna abundance is significantly correlated with herring density after the effect of spatial structure is removed (Mantel r  =   0.043, P  <   0.019).     

Climate‐induced environmental conditions influencing interannual variability of Mediterranean bluefin (Thunnus thynnus) larval growth

Daily growth variability of bluefin (Thunnus thynnus) larvae sampled in their Balearic Sea spawning grounds during the 2003–2005 spawning seasons was examined. Multi‐factorial ANOVA was applied to study the effects of environmental variables, such as temperature at 10 m depth (T10), microzooplankton dry weight (MDW) and protein/dry weight ratio (PROT/MDW) on larval growth. The 2003 bluefin tuna (BFT) larval cohort showed the fastest growth, recognizable from enhanced otolith and somatic mass increment compared to the 2004–2005 larval cohorts. The 2003 BFT larvae showed greater recent growth than the 2004–2005 BFT cohorts, which decreased in the last stages of development. Growth differences between the 2004 and 2005 larval cohorts were not significant. The environmental conditions between 2003 and 2004–2005 were highly contrasting as a result of the 2003 warming anomaly. Somatic and otolith growth rates (OGR) were significantly related to T10 and MDW, as well as to the PROT/MDW ratios. Nonetheless, the effect of T10 on OGR depended on the relative high (H) or low (L) levels of MDW and PROT/DW. Higher OGR was observed when T10 was high, MDW was low and PROT/DW was high. This environmental scenario conditions were met during 2003, which recorded the highest surface temperature and low planktonic biomass. Somatic growth, expressed as larval DW growth increase (DWGR), showed three‐factor significant interactions with T10*MDW*PROT/MDW, in which the two‐way interactions of MDW*PROT/MDW showed differences in the function of T10 levels.     

A spatiotemporal study of bacterial community profiles associated with Atlantic bluefin tuna larvae,Thunnus thynnus L., in three Mediterranean hatcheries

During the first 2 years of larval rearing trials with Atlantic bluefin tuna, survival was a challenging issue. As bacterial colonization of the gut has been shown to play a key role for other species, we studied the profiles of the microbiota associated with individual larvae at different stages in three distant hatcheries. The Bacterial Community Profile (BCP) was quantified based on PCR‐DGGE analyses of partial amplicons from 16S rDNA. Considerable individual variability in BCP was observed before onset of feeding, and the BCP did not show regular fluctuation during ontogenesis. Microalgae were added to the rearing tanks in two of the three hatcheries, but it was not possible to distinguish the effect of location from the effect of algal addition on BCP. In one hatchery, the larvae were reared either with algal addition or in mesocosm, but due to high individual variability, no significant difference in BCP was detected between the two groups. It was hypothesized that this variability was caused by differences in health, physiological status and developmental stage of the larvae. A practical conclusion from the study is the need to analyse a considerable number of individuals to reflect statistically significant differences between the microbial communities associated with rearing groups.     

Oceanographic changes and exploitation drive the spatio‐temporal dynamics of Atlantic bluefin tuna (Thunnus thynnus)

Atlantic bluefin tuna (ABFT) has always displayed spectacular changes in its spatial distribution, but the underlying mechanism of such variations still remains obscure. This study focuses on this challenging issue by scrutinizing the intriguing ‘Brazilian episode’ during which a large quantity of ABFT (a temperate species) was caught during the 1960s in the equatorial Atlantic. To investigate this event, we applied a niche model to an extensive data set of catch and environmental variables from 1960 to 2009. ABFT exhibited a remarkably large ecological niche, which matches well with our current knowledge of ABFT. Our results also depicted a high probability of ABFT occurrence in the South Atlantic and, more interestingly, favorable environmental conditions in the western equatorial Atlantic during the 1960s, but not later. ABFT could thus have migrated from their northern spawning grounds to the South Atlantic during the 1960s through the western equatorial Atlantic, playing the role of an ‘ecological bridge’. We argue that the rarity of ABFT in the southern Atlantic during the last four decades would result from the interaction of several processes, particularly oceanographic conditions, migratory behavior, density‐dependence, exploitation levels and population structure. Examination of the catch data further indicated that the fish caught in the equatorial Atlantic were from the western stock and we concluded that the lack of rebuilding of this stock could result from a regime shift due to the combination of oceanographic changes in the equatorial Atlantic and overfishing in the North Atlantic in the 1960s and 1970s.     

Putting the pieces together: Recent growth,nutritional condition,and mortality of Engraulis anchoita larvae in the Southwest Atlantic

Dynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.     

Turbulence effect on survival and feeding of pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> larvae,on the basis of a rearing experiment

ABSTRACT:   Physical conditions such as oceanic turbulence related to food availability are considered to be important factors affecting fish larval survival. Rearing experiments were conducted to elucidate the effects of turbulence on the survival and feeding rates during the initial feeding period of Pacific bluefin tuna Thunnus orientalis . Six levels of turbulence intensity were provided by changing flow rates from pipes set on the bottom of rearing tanks. The result showed a dome-shaped relationship between turbulence level and survival rate, in which the feeding rate appeared higher at a logged turbulence energy dissipation rate of −6.32, and decreased at both higher and lower turbulence levels. Compared with the turbulence intensity in the ocean, the optimal turbulence level for Pacific bluefin tuna larvae corresponded to the turbulence caused by sea surface winds with speeds of 4–12.5 m/s. The estimated optimal turbulence intensity for Pacific bluefin tuna larvae is comparable to that for yellowfin tuna Thunnus albacares .     

Are the long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) population related to environmental changes?

We tested whether synchronous, long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) trap catches, collected from the ancestral Mediterranean and Atlantic trap fishery, might be related to large‐scale environmental change. Nine time series of trap catches of more than 80 yr long were compared with long time series of three preselected environmental variables, i.e. the North Atlantic Oscillation (NAO), the Length of the Day Index (LOD, a proxy of the atmospheric circulation index) and the temperature. Spectral analyses of trap catches, LOD and temperature displayed similar spectra with peaks at low frequencies, whereas those of the NAO exhibited a broad band spectrum. Regression analyses and tests of correlation did not reveal any clear relationship between trap catches on the one hand and NAO and LOD on the other hand. In contrast, long‐term fluctuations in trap catches appear to be closely and negatively related to long‐term trends in temperature. Underlying processes that could explain such a relationship are discussed, with special focus on changes in migration patterns of the Atlantic bluefin tuna.     

Lessons from the past: investigating historical data from bluefin tuna fisheries

In 1963, the leading fisheries targeting Atlantic bluefin tuna ( Thunnus thynnus ) in the Norwegian Sea and North Sea suddenly collapsed without any warning. Little is known about this collapse and several hypotheses have been put forward, such as changes in migratory routes, recruitment failure or eradication of a sub-population: all of these hypotheses could result from natural causes and/or from overfishing. To help explain this mysterious event, an original data set of the main bluefin tuna fisheries of the 20th century, including total catch and size composition of the catch, has been compiled and analysed. The results reveal a strong and unambiguous link between the Nordic purse seine and Spanish trap fisheries during the 1950s and 1960s. However, this link vanished during the 1970s. In addition, the North-west Atlantic and Mediterranean trap fisheries appeared also to be partially connected to the Nordic fisheries. During the 1950s and 1960s, the main migration routes of bluefin tuna were probably from the Mediterranean spawning grounds and from the West Atlantic coasts to the Norwegian coast and North Sea, which were probably a key feeding ground at that time. The analyses also lead to the conclusion that interactions between environmental, trophic and fishing processes have probably affected bluefin tuna migration patterns which would have finally caused the Nordic fisheries collapse. This retrospective analysis finally leads to an original – albeit more speculative – hypothesis concerning Atlantic bluefin tuna population structure, therein conjectured as an assemblage of at least three sub-populations.     

Carrying capacity and survival strategy for the Pacific bluefin tuna, Thunnus orientalis, in the Western Pacific

The carrying capacity for the Pacific bluefin tuna at each life stage is estimated and its survival strategy is examined numerically, using a new method to define the hypothetical capacity, the standard population, and the search volumes that are necessary and are feasible for the tuna. The carrying capacity for the adult is estimated at 1–2 × 10⁶ individuals, which corresponds with 5–10% of the hypothetical capacity and is comparable with the maximum levels of the southern and the Atlantic bluefin tuna populations. It is hypothesized semiquantitatively that the migration at each life stage and the remarkable decrement of growth at 120 days and about 40 cm occur as an evolutionary response to population excess over the carrying capacity. It is also hypothesized semiquantitatively that the early larvae have minimal food available in the Subtropical Water and develop the predatory morphology, high growth rate, and high mobility, however, at the expense of a high mortality as an evolutionary response to the tuna spawning in the Subtropical Water. This method may be an available tool to not only investigate the carrying capacity and survival strategy of a specific fish species, but also predict when and in how much abundance the fish species occurs in a specific area of its habitat.     

Tuna and swordfish catch in the U.S. northwest Atlantic longline fishery in relation to mesoscale eddies

To analyze the effects of mesoscale eddies, sea surface temperature (SST), and gear configuration on the catch of Atlantic bluefin (Thunnus thynnus), yellowfin (Thunnus albacares), and bigeye tuna (Thunnus obesus) and swordfish (Xiphias gladius) in the U.S. northwest Atlantic longline fishery, we constructed multivariate statistical models relating these variables to the catch of the four species in 62 121 longline hauls made between 1993 and 2005. During the same 13‐year period, 103 anticyclonic eddies and 269 cyclonic eddies were detected by our algorithm in the region 30–55°N, 30–80°W. Our results show that tuna and swordfish catches were associated with different eddy structures. Bluefin tuna catch was highest in anticyclonic eddies whereas yellowfin and bigeye tuna catches were highest in cyclonic eddies. Swordfish catch was found preferentially in regions outside of eddies. Our study confirms that the common practice of targeting tuna with day sets and swordfish with night sets is effective. In addition, bluefin tuna and swordfish catches responded to most of the variables we tested in the opposite directions. Bluefin tuna catch was negatively correlated with longitude and the number of light sticks used whereas swordfish catch was positively correlated with these two variables. We argue that overfishing of bluefin tuna can be alleviated and that swordfish can be targeted more efficiently by avoiding fishing in anticyclonic eddies and in near‐shore waters and using more light sticks and fishing at night in our study area, although further studies are needed to propose a solid oceanography‐based management plan for catch selection.     

Schooling and migration of large pelagic fishes relative to environmental cues

A kinesis model driven by high-resolution sea surface temperature maps is used to simulate Atlantic bluefin tuna movements in the Gulf of Maine during summer months. Simulations showed that individuals concentrated in areas of thermal preference. Results are compared to empirical distribution maps of bluefin tuna schools determined from aerial overflights of the stock during the same time periods. Simulations and empirical observations showed similar bluefin tuna distributions along fronts, although interannual variations in temperature ranges occupied suggest that additional foraging factors are involved. Performance of the model is further tested by simulating the relatively large-scale annual north–south migrations of bluefin tuna that followed a preferred thermal regime. Despite the model's relatively simple structure, results suggest that kinesis is an effective mechanism for describing movements of large pelagic fish in the expansive ocean environment.     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Modeling environmental influence on Atlantic bluefin tuna bycatch by Mexican longliners in the Gulf of Mexico

Atlantic bluefin tuna (ABFT) stocks have been considered overfished over the last decades, especially the western stock, whose main spawning grounds are in the Gulf of Mexico (GoM). Despite the current measures implemented, spawner bycatch by the longline fleet targeting yellowfin tuna (YFT) may explain the lack of recovery of local stocks. This situation demands the implementation of appropriate spatiotemporal management strategies to minimize bluefin bycatch in the GoM, which involves knowledge in depth of its distribution and environmental forcing. Using catch and effort data from the Mexican commercial longline fleet with 100% scientific observer coverage from 1999 to 2012 and satellite derived environmental data, this study investigated the influence of environmental conditions on catch per unit effort (CPUE) of ABFT and YFT. General additive models (GAMs) were fitted using a negative binomial distribution and applying Akaike information criterion (AIC) to select the best model. Bluefin CPUE exhibited a marked seasonality, reaching higher values in February and March while YFT catches occurred throughout the year. Two main locations were identified with higher ABFT bycatch rates, Campeche Bay and the western‐central area of the GoM. Higher ABFT CPUE was significantly associated with areas with negative sea level anomalies and low sea surface temperatures, characteristic of cyclonic eddies. Instead, YFT CPUE showed a lesser environmental influence in its distribution. To our knowledge, the patterns shown in this study provide the first in‐depth approach to understand ABFT bycatch in Mexican waters, which will help in further development of adequate management strategies.     

Non‐parametric modeling reveals environmental effects on bluefin tuna recruitment in Atlantic,Pacific, and Southern Oceans

Environment–recruitment relationships can be difficult to delineate with parametric statistical models and can be prone to misidentification. We use non‐parametric time‐series modeling which makes no assumptions about functional relationships between variables, to reveal environmental influences on early life stages of bluefin tuna and demonstrate improvement in prediction of subsequent recruitment. The influence of sea surface temperature, which has been previously associated with larval growth and survival, was consistently detected in recruitment time series of bluefin tuna stocks that spawn in the Mediterranean Sea, the North Pacific, and the Southern Ocean. Short time series for the Gulf of Mexico stock may have precluded a clear determination of environmental influences on recruitment fluctuations. Because the non‐parametric approach does not require specification of equations to represent system dynamics, predictive models can likely be developed that appropriately reflect the complexity of the ecological system under investigation. This flexibility can potentially overcome methodological challenges of specifying structural relationships between environmental conditions and fish recruitment. Consequently, there is potential for non‐parametric time series modeling to supplement traditional stock recruitment models for fisheries management.     

Tracking shifts in Atlantic mackerel (Scomber scombrus) larval habitat suitability on the Northeast U.S. Continental Shelf

Climate change has altered the oceanographic environment and subsequently the habitats of marine species. Fish and invertebrate populations’ responses to habitat include movement with latitude and depth to remain within their fundamental niches. The northwest Atlantic mackerel (Scomber scombrus) population has fluctuated over the last century due in part to changes in the environment. We used species distribution models to understand the influence of the physical (temperature) and biological (zooplankton) environment on mackerel larval abundance, and how such relations have determined larval habitat suitability in the Northeast U.S. Shelf. Atlantic mackerel larval presence and abundance correlated with sea temperature and copepod abundances, suggesting that larval survival may be sensitive to specific temperatures and zooplankton prey. Predicted abundances were spatially interpolated to estimate Atlantic mackerel larval suitable habitat. Metrics for habitat quality indicate that the Mid‐Atlantic Bight has become less suitable over time. Since the 1970s, the proportion of Northeast U.S. Shelf suitable habitat located in the Mid‐Atlantic Bight has decreased, as southern New England and the western Gulf of Maine regions have become more suitable. Habitat suitability within the Northeast U.S. Shelf has shifted northeast: from the Mid‐Atlantic Bight‐southern New England border towards the northeast portion of southern New England. While total Northeast U.S. Shelf habitat suitability has decreased since the 1970s, the decline in the time series trend was not statistically significant. Thus, while select ecoregions have decreased in habitat suitability, larval habitat does not appear to be the only contributor to decreases in the U.S. Atlantic mackerel contingent.