Spawning and transport dynamics of Atlantic menhaden: inferences from characteristics of immigrating larvae and predictions of a hydrodynamic model

We examined patterns of abundance, age and spawning date distributions of Atlantic menhaden Brevoortia tyrannus larvae immigrating during two seasons through three North Carolina inlets—Oregon, Ocracoke and Beaufort—to elucidate their spawning and transport dynamics. These patterns were examined in conjunction with corresponding predictions from a three-dimensional, wind-and tide-driven hydrodynamic model. Larvae immigrating through different inlets showed consistent similarities as well as marked differences in temporal patterns of abundance, spawning dates and transport times. Intraseasonal patterns in abundance and spawning date distributions among inlets suggest that, in both study years, the spatio-temporal dynamics of menhaden immigration were driven by large-scale patterns along the Atlantic coast, rather than by localized variation in spawning activity. Interannual differences in the temporal patterns of spawning dates and larval immigration indicate interannual differences in transport dynamics and/or the spatial-temporal distribution of spawning. When the spawning locations predicted by the hydrodynamic model are interpreted in conjunction with advanced very high resolution radiometer sea-surface temperature information, the results are consistent with the limited historical information available on spatio-temporal distribution of Atlantic menhaden eggs and larvae. The transport model also predicted distributions of arrival times for immigrating larvae that were comparable in range and variability with observed patterns. Our use of data from immigrating larvae, coupled with a hydrodynamic transport model and sea-surface temperatures, allowed us to uncover relationships between spatio-temporal patterns of Atlantic menhaden spawning and transport dynamics that could not have been identified by either approach alone.     

Eulerian views of layered water currents, vertical distribution of some larval fishes, and inferred advective transport over the continental shelf off North Carolina, USA, in winter

Currents that effect the shoreward transport of the larvae of estuarine-dependent fishes spawned in winter in Onslow Bay, North Carolina, USA, were driven by winds and pressure gradients, and influenced by the Gulf Stream. Aside from storms, winds over the continental shelf in Onslow Bay blew predominantly alongshore with velocities approaching 14 m s^-1 during February and March 1986, and January and February 1989. Water masses and currents observed at two current-meter moorings, one at mid-shelf and the other on the outer shelf, reflected the onshore (or offshore) advection of interior water in compensation for the offshore (or onshore) advection of wind-driven surface water. Winds and currents reversed direction approximately every 4 to 6 days. The larvae of Atlantic menhaden, Brevoortia tyrannus , spot, Leiostomus xan- thurus, and Atlantic croaker, Micropogonias undulatus , were most abundant in 17–19^oC and 20–21^oC water of the outer shelf and Gulf Stream fronts. There was little indication of diel vertical migration; larval Atlantic menhaden were most abundant in mid- and surface water, while spot and Atlantic croaker were most abundant in mid- and deep water. Given this distribution, the inferred advective transport of larvae was at times onshore, but at other times it was offshore. Within a spawning season, the prevalence of either reciprocation could determine the number of larvae that reach coastal inlets.     

Atlantic menhaden recruitment to a southern estuary: defining potential spawning regions

Atlantic menhaden ( Brevoortia tyrannus ) is an estuarine-dependent fish that spawns in coastal waters of the Middle and South Atlantic Bights. Circulation modelling studies of larval transport suggest that recruitment of larvae into the Albemarle-Pamlico Estuarine System, North Carolina, is linked to dynamics on the shelf from New York to South Carolina. Field-collected menhaden egg data (from MARMAP and SABRE) define a range of temperatures within which menhaden eggs have been found. In this study we refine the transport model-predicted spawning grounds for the 1994–95 season by using satellite-derived sea surface temperature data to highlight regions that are outside the observed spawning temperature range. We also use transport pathways leading from source locations to the estuarine system to characterize the temperature field experienced by particles/larvae during their spawning-ground to inlet transit. The modelled nearshore location of source regions agrees well with MARMAP and SABRE egg data, and points to the importance of understanding biological and physical linkages between the Middle and South Atlantic Bights. The combination of modelled transport and synoptic temperature maps can provide useful guidance to future sampling efforts as well as help refine our understanding of menhaden ecology.     

Predicting the dispersion of sprat larvae (Sprattus sprattus (L.)) in the German Bight

Sprat (Sprattus sprattus (L.)) larval dispersal in the German Bight is predicted with a model system consisting of two three-dimensional circulation models and a three-dimensional transport model. Horizontal distribution data for specific length classes of larvae, obtained from field surveys carried out in the German Bight during summer 1991, are used as initial conditions for the starting points of the tracers in the transport model. Sprat larval distributions are predicted and are compared with distributions of the appropriate length class of larvae observed during a subsequent cruise about 3 weeks later. The predicted larval (tracer) distributions compare favourably to observed larvae distributions in the inner model areas but not in the areas close to the coast. Factors contributing to inaccurate predictions are uncertainties in horizontal and vertical larval distributions as well as the model grid resolution, which is too coarse in coastal areas.     

Larval group differentiation in Atlantic cod (Gadus morhua) inside and outside the Gullmar Fjord

The spatial and temporal occurrence of pelagic fish stages and their biological variability may affect their dispersal and survival, and ultimately fish recruitment. We collected Atlantic cod larvae at one station inside and at one station outside the Gullmar Fjord, eastern Skagerrak, in order to investigate small-scale larval group differentiation. Rectangular midwater trawl hauls were taken every 6 h (during 24 h) from three separate depth intervals between the surface and 70 m depth. About 80% and 20% of all larvae occurred above the halocline at the Fjord station and the Coastal station, respectively. Hatching (at both stations) occurred from the 3rd week in February to the 1st week in May, indicating that cod larvae were present for at least 5 months (from late February to early August). The length and hatch date frequency distributions of larvae from the surface layer were unimodal inside the fjord but bimodal outside the fjord. Analyses of seven microsatellite DNA loci indicated that larvae collected inside the fjord (where local spawning occurs) were genetically distinct from larvae sampled on the outside (F_ST = 0.0026). The two age cohorts outside the fjord were not, however, genetically different, nor were larvae collected at different depths. We conclude that small-scale variability of vertical concentration and larval life history variability should have consequences for interpreting models of larval dispersal and survival, and subpopulation structure analyses.     

Macroscale drivers of Atlantic and Gulf Menhaden growth

The 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.     

Vertical distribution and migration of fish larvae in the NW Iberian upwelling system during the winter mixing period: implications for cross‐shelf distribution

The vertical distribution and vertical migrations of fish larvae and implications for their cross‐shelf distribution were investigated in the northern limit of the NE Atlantic upwelling region during the late winter mixing period of 2012. The average positive values of the upwelling index for February and March of this year were far from normal, although the average hydrographic conditions during the period of study were of downwelling and the water column was completely mixed. Fish larvae, most in the preflexion stage, were concentrated in the upper layers of the water column and their distribution was depth stratified, both day and night. However, the larval fish community was not structured in the vertical plane and fish larvae did not show significant diel vertical migration (DVM), although five species showed ontogenetic vertical migration. In regions of coastal upwelling and in the absence of DVM, the location of fish larvae in the water column is crucial for their cross‐shelf distribution. Thus, the cross‐shelf distribution of the six most abundant species collected in this study can be explained by the surface onshore flow associated with coastal downwelling, retaining larvae of the coastal spawning species with a relatively shallow distribution in the shelf region and transporting larvae of slope spawning species onto the shelf. The wide vertical distribution shown by larvae of the offshore spawning species could be an adaptation of these species to ensure that some larvae reach the inshore nursery areas.     

Mechanistic links between climate and fisheries along the east coast of the United States: explaining population outbursts of Atlantic croaker (Micropogonias undulatus)

Climate has been linked to variation in marine fish abundance and distribution, but often the mechanistic processes are unknown. Atlantic croaker (Micropogonias undulatus) is a common species in estuarine and coastal areas of the mid‐Atlantic and southeast coasts of the U.S. Previous studies have identified a correlation between Atlantic croaker abundance and winter temperatures in Chesapeake Bay, and have determined thermal tolerances of juveniles. Here we re‐examine the hypothesis that winter temperature variability controls Atlantic croaker population dynamics. Abundance indices were analyzed at four life history stages from three regions along the east coast of the U.S. Correlations suggest that year‐class strength is decoupled from larval supply and is determined by temperature‐linked, overwinter survival of juveniles. Using a relation between air and water temperatures, estuarine water temperature was estimated from 1930 to 2002. Periods of high adult catch corresponded with warm winter water temperatures. Prior studies indicate that winter temperature along the east coast is related to the North Atlantic Oscillation (NAO); variability in catch is also correlated with the NAO, thereby demonstrating a link between Atlantic croaker dynamics, thermal limited overwinter survival, and the larger climate system of the North Atlantic. We hypothesize that the environment drives the large‐scale variability in Atlantic croaker abundance and distribution, but fishing and habitat loss decrease the resiliency of the population to periods of poor environmental conditions and subsequent weak year classes.     

Larval transport during winter in the SABRE study area: results of a coupled vertical larval behaviour–three-dimensional circulation model

A three-dimensional circulation model was used in conjunction with larval fish vertical behaviour models to study the interaction between larval vertical distribution, advection and the outcome of larval transport along the central portion of the east coast of the United States. The circulation model was forced by tides, a northern boundary inflow, and winds. Vertical behaviour models were developed for Atlantic menhaden ( Brevoortia tyrannus ) and spot ( Leiostomus xanthurus ). The purpose of this modelling effort was to investigate the transport pathways of Atlantic menhaden and spot larvae from offshore spawning grounds to estuarine nursery habitats. The coupled circulation and behavioural model demonstrated the importance of along-shelf transport in what is generally thought to be a 'cross-shelf' problem. Cross-shelf transport was associated with bathymetric features, such as shoals. Both physical (e.g. wind) and biological (e.g. changes in larval behaviour) events were responsible for many of the observed patterns in larval transport. Overall, larval transport was determined by circulation but was modified by larval vertical distributions.     

Evaluating diel, ontogenetic and environmental effects on larval fish vertical distribution using Generalized Additive Models for Location, Scale and Shape

Changes in ichthyoplankton vertical distributions can have important consequences with respect to larval transport and survivorship, yet determining the relative importance of environmental influences on vertical migrations in a statistically meaningful framework remains challenging. Here we use Generalized Additive Models for Location, Scale and Shape (GAMLSS) and Akaike Information Criteria (AIC) to model the vertical distribution of larval Urophycis regia collected over a 108-h time series on the Mid-Atlantic Bight shelf. Depth was the response variable weighted by two measures of larval abundance: concentrations (number 100 m⁻³) and proportions at depth. Mean and variance of depth were modeled as a function of time, wind stress, current velocity, water column stratification and ontogeny. Model results indicated a large effect of stage for both concentration- and proportion-based analyses. Subsequent and separate analyses on preflexion and postflexion U. regia indicated a differential response to the environmental parameters based on ontogeny. Model results suggested preflexion U. regia do not have a diel pattern in vertical distribution, but do avoid areas of high surface turbulence related to wind stress. In contrast, postflexion larvae have a significant diel pattern of vertical distribution mediated by surface turbulence (increased variance). The statistical approaches applied here offer the potential to evaluate the effect of multiple factors on vertical distribution and have provided significant insight into the factors that influence the vertical distribution of spotted hake larvae.     

Simulating the dispersion of vertically migrating sprat larvae (Sprattus sprattus (L.)) in the German Bight with a circulation and transport model system

A model system consisting of two three-dimensional circulation models and a three-dimensional transport model is used to simulate the dispersal of sprat larvae (Sprattus sprattus (L.)) in the German Bight. A Northwest European shelf sea model simulates the currents of the North Sea and provides sea surface elevation data for the open boundaries of the German Bight circulation model. The German Bight circulation model has a horizontal grid resolution of 2.75 km and a vertical resolution of 5 m except for the bottom layer. The driving forces of the circulation models are the M2-tide, six-hourly time-dependent wind stress and air pressure fields as well as monthly climatological density fields. The simulated currents serve as input to the transport model. The model area, grid size and the vertical resolution of the transport model are in accordance with the German Bight circulation model. The transport model simulates advection and diffusion using a Monte Carlo method. Furthermore it incorporates a simulation of active vertical movement of the larvae. The vertical migration pattern is dependent on the time of day and size of the larvae and is based on field data from the German Bight. Horizontal larvae distribution data, gained from two out of five field surveys carried out in the German Bight during spring and summer 1991, are used as initial values for the starting points of the tracers in the transport model. Simulated tracer distributions are compared with larval distributions observed during subsequent cruises about 3 weeks later. Discrepancies and similarities between tracer and larval distributions are discussed.     

Population structure and movement patterns of blackbelly rosefish in the NE Atlantic Ocean (Azores archipelago)

Blackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809) is one of the most important species of the demersal/deep‐water assemblages fished in the NE Atlantic Ocean (Azores archipelago). However, there is insufficient information about the stock structure of this species to support analytical resource assessments and it is currently managed with a precautionary approach. Here, we examine the depth and temporal distribution, size composition, sex, and movement patterns of blackbelly rosefish in order to test the hypothesis that the stock structure in the Azores region comprises different local management units (MUs). We also evaluate annual abundance indices and size composition from scientific surveys and commercial landings over the past c. 25 years for an assessment of the species' vulnerability to bottom longline fishing pressure. The greatest abundance occurred in seamount areas at 350–800 m depth. Larger individuals were mainly found in deeper waters, and no sexual segregation by depth was observed. Tagging results indicated a strongly sedentary behavior and an intraregional separation among populations. Although the abundance pattern and size composition were very similar over time, this species is particularly vulnerable to overfishing due to its biological characteristics (long life, large size, late maturity, slow growth, and low mortality rate). Proper monitoring and management of its exploitation should be a priority. Exploratory analysis for analytical assessment should be performed under the assumption of local MUs. Further oceanographic research is needed to understand larval transport and mixing of populations.     

Towards a more complete understanding of the life cycle of brown shrimp (Crangon crangon): modelling passive larvae and juvenile transport in combination with physically forced vertical juvenile migration

In this study we developed and utilized a complex model approach to investigate the impact of stage‐specific transport processes on the development and spatial distribution of brown shrimp (Crangon crangon) post‐larvae and juveniles in the German Bight. First, we focused on drift processes during the pelagic larval stage by coupling an individual‐based model for egg and larval development ‘off‐line’ to a 3D hydrodynamic model utilizing the Lagrangian method. Secondly, we investigated tidal‐induced transport processes after juvenile settlement. To determine the tidal cycle, the model coupling was accomplished ‘on‐line’ by resolving the individual‐based model and hydrodynamic model with the same time step. The vertical migration of juveniles, a prerequisite for the selective tidal stream transport (STST), was modelled as a sub‐grid scale physical process (balance of forces: gravitation, buoyancy, Stoke’s friction and dynamic uplift) and considered complex particle dynamics. We applied the model to test temperature and salinity cues as possible tidal indicators utilized by juvenile brown shrimp. Our results indicated that transport processes could significantly change the timing and spatial distribution of post‐larval abundance. We also showed that the small‐scale hydrodynamic forcing acting on the bodies of juvenile brown shrimps was sufficient to account for the vertical migration required to use STST. For both investigated tidal cues STST performing juvenile brown shrimp were transported on‐shore. A faster and more continuous STST was calculated for the salinity cue, resulting in larger abundances of brown shrimp in estuarine areas.     

Distribution patterns of larval myctophid fish assemblages in the subtropical–tropical waters of the western North Pacific

We examined larval myctophid fish assemblages and their distribution patterns, based on discrete depth sampling. Samples were collected at 19 stations along a transect that crossed the subtropical–tropical waters of the western North Pacific. In total, we collected 27 189 larvae of 40 myctophid species or types, belonging to 15 genera. Three assemblages were recognized, based on their species composition: Kuroshio Axis (KuA), Kuroshio Countercurrent (KCC), and Subtropical Countercurrent–North Equatorial Current (SCC–NEC) assemblages. The distributions of these assemblages were well defined by the positions of the KuA and the Subtropical Convergence. Each species had a specific distribution depth, and none showed diel vertical migration. Larvae of the subfamily Lampanyctinae were distributed in shallower waters (0–50 m) than larvae of the subfamily Myctophinae (50–150 m). Larvae of the same species were distributed at lower depths in the SCC–NEC area than in the KCC area. This corresponded to the abundance of chlorophyll a, which would reflect abundance of prey organisms such as copepod nauplii and copepodites.     

Predator–prey analysis of striped bass and Atlantic menhaden in upper Chesapeake Bay

Between 1997 and 2000, an outbreak of skin lesions and observations of emaciated striped bass, Morone saxatilis (Walbaum), in upper Chesapeake Bay were attributed to a perceived shortage of its main prey, Atlantic menhaden, Brevoortia tyrannus Latrobe. Abundance estimates, Atlantic menhaden consumption per recruit analysis (modified yield‐per‐recruit), bioenergetics analysis and predator–prey theory were combined to explore whether an imbalance between striped bass and Atlantic menhaden in upper Chesapeake Bay was plausible. Reduced fishing mortality and higher size limits that underpinned the effort to restore striped bass during the 1980s and 1990s lead to more abundant and larger striped bass in upper Chesapeake Bay, increasing predatory demand for forage‐sized Atlantic menhaden, the abundance of which declined to a historic low. Nominal losses of age 0–2 Atlantic menhaden to harvest and potential striped bass predation exceeded supply after 1998. The outbreak of lesions in upper Chesapeake Bay striped bass coincided with increased variation in weight‐at‐length, decreased length‐at‐age, and decreased presence of Atlantic menhaden in diets. Decreased attack success, inferred from a 97% decline in ratios of forage‐sized Atlantic menhaden to striped bass between 1983 and 1998, would have expected to have been followed by a deterioration of striped bass nutritional state. Transmission of disease would have been aided by high density of striped bass in poor nutritional condition residing in degraded habitat (Chesapeake Bay was the most hypoxic estuary in the mid‐Atlantic region in the late 1990s). These problems suggest that striped bass exceeded their carrying capacity in Chesapeake Bay during the late 1990s.     

How fast can the European eel (Anguilla anguilla) larvae cross the Atlantic Ocean?

The migration duration of European eel ( Anguilla anguilla ) larvae (leptocephali) from the spawning areas in the Sargasso Sea to the European continental shelf remains highly controversial, with estimates varying from 6 months to more than 2 yr. We estimated the fastest migration period and the shortest distance travelled by eel larvae by simulating Lagrangian particles released in the Sargasso Sea and by simulating a range of larval behaviours (fixed-depth drift, vertical diurnal migration and active-depth selection to maximize current velocity). This enabled us to compute (i) a passive drift speed, and (ii) a hypothetic swimming speed needed for European eel larvae to cross the Atlantic in 6 months (i.e., the migration duration estimated from otolith daily growth increments). Our results show that the minimum travel time for an eel larva that is passively drifting was 10 months and 3 days. Active behaviours (vertical diurnal migration and rheotaxis) paradoxically increased the migration period. We found that for leptocephali to cross the Atlantic Ocean in 6 months, they would need to swim a minimum of 3.4 body lengths per second for 8200 km. No larvae have been observed with such swimming capabilities. These results provide evidence that leptocephali cannot cross the Atlantic in 6 months.     

Distribution of the early life stages of small yellow croaker in the Yangtze River estuary and adjacent waters

The horizontal distribution of the early life stages of small yellow croaker Larimichthys polyactis in the Yangtze River estuary and its adjacent area was investigated through six ichthyoplankton surveys conducted during the period of mid-April to mid-July 2015. A total of seven eggs and 2461 larvae and juveniles of small yellow croaker were collected. Abundance of the specimens was highest in mid-May and lowest in mid-July. The composition of the different development stages of small yellow croaker varied among the six cruises, although post-flexion larvae and juveniles dominated the ichthyoplankton collection in each cruise. Specimens at different development stages showed different distribution patterns in the study area. The eggs, yolk-sac and pre-flexion larvae were mainly collected at stations with depth exceeding 30 m, while post-flexion larvae and juveniles were mainly distributed in the relatively shallow waters near to the mouth of the Yangtze River. In conclusion, the study suggested that the study area had largely lost the ecological function to support small yellow croaker spawning, although it could still serve as nursery ground for the species.     

Processes controlling retention of spring‐spawned Atlantic cod (Gadus morhua) in the western Gulf of Maine and their relationship to an index of recruitment success

Atlantic cod, Gadus morhua, harvested in US waters are currently managed as a Gulf of Maine stock and as a stock comprising Georges Bank and southern New England populations. Over the past two and a half decades, success of age‐1 recruitment to the Gulf of Maine stock has varied by more than an order of magnitude. To investigate the hypothesis that this variation is related to variation in the transport of larval cod to nursery areas, we carried out model simulations of the movement of planktonic eggs and larvae spawned within the western Gulf of Maine during spring spawning events of 1995–2005. Results indicate that the retention of spring‐spawned cod, and their transport to areas suitable for early stage juvenile development, is strongly dependent on local wind conditions. Larval cod retention is favored during times of downwelling‐favorable winds and is least likely during times of upwelling‐favorable winds, during which buoyant eggs and early stage larvae tend to be advected offshore to the Western Maine Coastal Current and subsequently carried out of the Gulf of Maine. Model results also indicate that diel vertical migration of later stage larvae enhances the likelihood of retention within the western Gulf of Maine. Consistent with model results is a strong correlation between age‐1 recruitment success to the Gulf of Maine cod stock and the mean northward wind velocity measured in Massachusetts Bay during May. Based on these findings, we propose a wind index for strong recruitment success of age‐1 cod to the Gulf of Maine stock.     

Variation in DVM behaviour of juvenile and adult pearlside (Maurolicus muelleri) linked to feeding strategies and related predation risk

In the Norwegian fjord Masfjorden, different developmental stages of the mesopelagic planktivore Maurolicus muelleri form vertically separate sound scattering layers (SSLs) and in late autumn display different diel vertical migration (DVM) behaviour. Post‐larvae and juvenile fish perform normal crepuscular DVM, whereas the large majority of adults remain at depth throughout the diel period. In this study we examined the stomach contents of juvenile and adult fish caught at different times and depths during a 24‐h period in autumn. The different DVM behaviour of these two SSLs in addition to a shallow layer believed to be composed of post‐larvae is explained with a model for visual foraging in aquatic environments that uses gradients in vertical light intensity and copepod density and size as input variables. Field data revealed that vertically migrating juveniles distributed at a higher ambient light intensity and on average consumed 25 times more copepods than non‐migrating adult fish. The model showed that juveniles experienced a 15 times higher prey encounter rate and a higher level of predation risk than non‐migrating adults, and that the energetic benefits for post larvae and juveniles from prolonged feeding in a nearly constant and brighter environment outweigh the associated predation risk. The model also suggests that the visual detection range of piscivore predators is relatively more limited by the turbid surface water than that of their prey, which provide the post‐larva and juvenile life‐stages of M. muelleri a window of reduced visual predation near the surface.     

Proteome profile comparison of two differently fed groups of Atlantic cod (Gadus morhua) larvae

Proteome analysis was used to study the effects of feeding early Atlantic cod (Gadus morhua) larvae with a saithe (Pollachius virens) protein hydrolysate (SPH). Protein hydrolysates have previously been shown to beneficially affect fish larval development. Feeding was initiated on day 2 post hatch (ph) or as soon as the larvae opened their mouth and the protein expression was monitored 4 days later or in 6‐dph cod larvae. The results demonstrated changes in the abundance of 13 protein spots in the cod larvae fed SPH. Of these, seven protein spots were up‐regulated and six protein spots showed down‐regulation. Five of the up‐regulated proteins in cod larvae are known to be involved in energy metabolism. A few early larval specific proteins were down‐regulated in the SPH‐fed cod larvae possibly because of an enhanced development in this group relative to the control group. Two trypsin isoforms were detected within the cod larval proteome. The detection of the trypsin spots was made possible by co‐electrophoresis of known cod trypsins with the cod larval protein extract. Surprisingly, no difference in trypsin content was observed between the SPH‐fed and the control larval groups.