From spawning grounds to the estuary: using linked individual-based and hydrodynamic models to interpret patterns and processes in the oceanic phase of Atlantic menhaden Brevoortia tyrannus life history

Present theory suggests that population regulation in marine fishes cannot be resolved until an understanding of the processes involved in shaping the overall distribution (the number of populations, geographical extent, mean abundance and temporal changes in abundance) is developed. Here, we present a step toward understanding Atlantic menhaden population patterns, by studying processes in the Middle and South Atlantic Bights, which shape those patterns. We use individual-based and hydrodynamic models to reinterpret the 'mechanics' of the menhaden life history, and put forward several potentially testable hypotheses. The success of the menhaden reproductive strategy seems to depend on the seasonal changes in the mean flow field of the Middle and South Atlantic Bights, suggesting that their life history may have been strongly structured by the regional physics of the system. Because the annual menhaden migration is size-based and spawning occurs throughout the population's range, the size distribution of the adult population may influence the supply of larvae to particular estuaries along the coast. Recruitment of larvae into Delaware and Chesapeake Bays may be dependent on spawning to the north of the bays' mouths, owing to coastline shape and orientation in the vicinity of the bays. Our results suggest that management of this resource might be improved by consideration of the spatial and temporal variability in both the biological and the physical system.     

Physical oceanography of the North Carolina continental shelf during the fall and winter seasons: implications for the transport of larval menhaden

The circulation over the continental shelf off the southern Middle Atlantic Bight (MAB) and northern South Atlantic Bight (SAB) is examined for the fall and winter periods. Observational data are compared with results from a three-dimensional numerical model to identify the dominant processes on the shelf. By considering wind-forcing, tides, and a specified upstream inflow (into the MAB), the observed and modelled flow fields are in close agreement in the mid- and inner shelf regions. The resulting larval drift indicates a seasonal dependence of transport pathways from spawning grounds to estuarine nursery areas for menhaden larvae and other offshore-spawning estuarine-dependent fish. Specifically, the physical oceanography of the MAB and SAB during the fall and winter months suggests a north-to-south shift in spawning areas providing recruits to the Carolina estuaries, in agreement with the observed migration of the spawning populations.     

Physical oceanography of the North Carolina continental shelf during the fall and winter seasons: implications for the transport of larval menhaden

The circulation over the continental shelf off the southern Middle Atlantic Bight (MAB) and northern South Atlantic Bight (SAB) is examined for the fall and winter periods. Observational data are compared with results from a three-dimensional numerical model to identify the dominant processes on the shelf. By considering wind-forcing, tides, and a specified upstream inflow (into the MAB), the observed and modelled flow fields are in close agreement in the mid- and inner shelf regions. The resulting larval drift indicates a seasonal dependence of transport pathways from spawning grounds to estuarine nursery areas for menhaden larvae and other offshore-spawning estuarine-dependent fish. Specifically, the physical oceanography of the MAB and SAB during the fall and winter months suggests a north-to-south shift in spawning areas providing recruits to the Carolina estuaries, in agreement with the observed migration of the spawning populations.     

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.     

The South Atlantic Bight Recruitment Experiment: introduction and overview

The South Atlantic Bight Recruitment Experiment (SABRE) brought together a interdisciplinary team of scientists to conduct research to enhance our understanding of the relationship between variation in environmental factors and the variable recruitment of 'estuarine dependent' fishes within the SAB. The project sought to develop a new fusion of government and academic scientists, each possessing unique skills, to address the difficult problem of recruitment variability in fishes. This fusion required the development of appropriate and at that time novel management and administrative strategies. SABRE initially focused on recruitment dynamics of Atlantic menhaden, Brevoortia tyrannus , in the South Atlantic Bight, but expanded over time to include several estuarine-dependent species and much of the Middle Atlantic Bight as well. The project was conducted from 1991 to 1997 and resulted in a substantial improvement in our understanding of the life history and ecology of Atlantic menhaden and the potential constraints upon its recruitment. SABRE also contributed to our understanding of the physical oceanography of the western North Atlantic shelf and adjacent coastal inlets and the implications of physical dynamics upon the potential pathways for larval transport.     

Applications of SABRE to research and management

In this paper, we highlight the major results from the SABRE programme and applications to research and management. In particular, SABRE provided new scientific insights into the fisheries oceanography of the estuarine-dependent fishes of the South Atlantic Bight. Although we concentrated our efforts on Atlantic menhaden, we also gained insights on the coupling of physics to biology in the early life history of a number of marine fishes. Larval transport from spawning sites to and through barrier island inlets is now better understood. Analysis of menhaden population dynamics suggests survival in the late larval/early juvenile stage is particularly important to population growth. This phase of the life history appears likely to present a bottleneck to recruitment for Atlantic menhaden. We also made a number of technological breakthroughs which are already being applied elsewhere in research and assessments including the Continuous, Underway Egg Sampler (CUFES), enzyme-based approaches to evaluating condition of individual larvae and various physical and biological modelling innovations. Our experiences establishing and managing the SABRE research team also provide insights into one model for promoting multidisciplinary research in fisheries oceanography. Throughout SABRE, we have sought an open exchange of information and insights from a wide variety of researchers and environmental managers. We hope the synthesis provided here continues that dialogue.     

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.     

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.     

Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina

The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden ( Brevoortia tyrannus ) from 3-m depth off North Carolina in winter 1993–94 and 1994–95. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a . The maximal concentration of eggs was 346 eggs m⁻³. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid-shelf fronts (17–23°C, 36.0–36.4‰). Unexpectedly, eggs were found almost exclusively in water of 20–60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modelling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favourable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.     

A continuous, underway fish egg sampler

We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with areal abundance estimated from vertically integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993–94, had a linear scale of 5–10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may be related to bathymetry. CUFES is now being used to estimate spawner biomass by the daily egg production method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sample by CUFES.     

Reproductive biology of bluefish (Pomatomus saltatrix) along the East Coast of the United States

The reproductive biology of bluefish (Pomatomus saltatrix) along the U.S. East Coast is examined from a collection 1437 females sampled from nearshore to the continental slope and from Florida to New York over a period of 3 years (2001–2003). In most years concurrent sampling along the coast was conducted over spring and summer months to resolve the initiation of spawning. We examined the spawning location, pattern and timing, and calculated the fecundity of fish from 600 to 840 mm in length. Based on macro- and microscopic analysis of female gonads, bluefish are multiple spawners with indeterminate fecundity. The presence of all stages of development in fully mature ovaries further indicates that bluefish have asynchronous oocyte development. Mean age at first maturity for female bluefish was 1.90 years and 480 mm total length. Mean batch fecundity was 402,247 eggs and ranged from 114,513 to 920,746 eggs, depending on age and weight. Direct observation of gonads showed imminent spawning in Florida and North Carolina during March to April, and from April to August from Virginia to New York. Given the progression of oocyte development over the range of space and time we sampled, we suggest that bluefish exhibit continuous spawning during their migration from the South Atlantic Bight (SAB) to Middle Atlantic Bight (MAB).     

Volitional Spawning of Black Sea Bass Centropristis striata Induced with Pelleted Luteinizing Hormone Releasing Hormone-Analogue

The black sea bass is a high‐value marine serranid and is a prime candidate for intensive cultivation. Reliable methods for controlled spawning are needed to accelerate the development of hatchery technologies that result in mass production of healthy juveniles. During 1998–2001, spawning studies were conducted at The University of North Carolina at Wilmington (UNCW) and at the South Carolina Department of Natural Resources (SCDNR), Charleston, using pelleted luteinizing hormone releasing hormone analogue (LHRH‐a). From April through July 2001, 28 vitellogenic‐stage females, with mean oocyte diameters (MOD) ranging from 277–448 μm, were implanted with a 95% cholesterol‐5% cellulose pellet containing LHRH‐a (‐50 μg/kg body wt) at UNCW. In 10 individual spawning trials, females with MOD of 305–448 μm and maximum oocyte diameter × 475 μm spawned volitionally beginning 2–3 d post‐implantation (PI) and continued spawning over an average of 1.9 d (range = 1–4 d). Individual females released a mean total of 149,000 eggs (117,000 eggs/kg) with a mean buoyancy rate of 40.5% (floaters). Fertilization and hatching rates were 98% and 27.2% of floaters, respectively, yielding 14,600 yolksac larvae/female (12,600 yolksac larvae/kg body wt), and overall egg viability averaged 8.9%. In eight group spawning trials (2–3 females/group), average performance of females, including fecundity (103,800 eggs/female; 105,500 eggs/kg body wt), buoyancy rate (42.5%), fertilization and hatching rates (97.7% and 24.3% of floaters), numbers of yolksac larvae produced (10,900 yolksac larvae/female; 10,100 yolksac larvae/kg body wt), and overall egg viability (10.6%) was comparable to what was seen in individual spawning trials. From 1998–2000, a total of 58 vitellogenic stage (70% of oocytes 500 pm) females were implanted with pelleted LHRH‐a (‐50 μg/kg body wt) in nine group spawning trials (2–19 females/group) at SCDNR. Volitional spawning typically began 18–42 h PI and recurred every 1–3 d for an average duration of 9 d. Female groups released a mean of 560,000 eggs (84,000/female; 132,000/kg body wt) over the spawning period, with mean buoyancy rate of 25.7% floaters. Fertilization and hatching rates were 17.7% and 11.6 % of floaters, respectively, yielding 4,300 yolksac larvae/female (4,600 yolksac larvae/kg body wt). Overall egg viability was 2.9%. Captive wild‐caught black sea bass were induced to undergo repetitive volitional spawning by implantation of pelleted‐LHRH‐a, consistent with a multiple clutch group synchronous pattern of ovarian development. Group spawning appears to be a practical way to compensate for variable fecundity and egg viability of individual females. Research is needed to identify optimum hormone treatments and eligibility requirements.     

Atlantic coast feeding habits of striped bass: a synthesis supporting a coast-wide understanding of trophic biology

The recent increase in the Atlantic coast population of striped bass, Morone saxatilis (Walbaum), prompted managers to re‐evaluate their predatory impact. Published and unpublished diet data for striped bass on the Atlantic Coast of North America were examined for geographical, ontogenetic and seasonal patterns in the diet and to assess diet for this species. Diets of young‐of‐the‐year (YOY) striped bass were similar across the Upper Atlantic (UPATL), Chesapeake and Delaware Bays (CBDEL) and North Carolina (NCARO) areas of the Atlantic coast where either fish or mysid shrimp dominate the diet. For age one and older striped bass, cluster analysis partitioned diets based on predominance of either Atlantic menhaden, Brevoortia tyrannus (Latrobe), characteristic of striped bass from the CBDEL and NCARO regions, or non‐menhaden fishes or invertebrates, characteristic of fish from the UPATL, in the diet. The predominance of invertebrates in the diets of striped bass in the UPATL region can be attributed to the absence of several important species groups in Northern waters, particularly sciaenid fishes, and to the sporadic occurrences of Atlantic menhaden to UPATL waters. In all regions, across most seasons and in most size classes of striped bass, the clupeiod fishes; menhaden, anchovies (Anchoa spp.) and river herrings (Alosa spp,) and Atlantic herring, Clupea harengus L., dominated the diets of striped bass above the first year of life.     

Simulation of mackerel (Scomber scombrus) recruitment with an individual-based model and comparison with field data

An individual‐based model (IBM) for the simulation of year‐to‐year survival during the early life‐history stages of the north‐east Atlantic stock of mackerel (Scomber scombrus) was developed within the EU funded Shelf‐Edge Advection, Mortality and Recruitment (SEAMAR) programme. The IBM included transport, growth and survival and was used to track the passive movement of mackerel eggs, larvae and post‐larvae and determine their distribution and abundance after approximately 2 months of drift. One of the main outputs from the IBM, namely distributions and numbers of surviving post‐larvae, are compared with field data as recruit (age‐0/age‐1 juveniles) distribution and abundance for the years 1998, 1999 and 2000. The juvenile distributions show more inter‐annual and spatial variability than the modelled distributions of survivors; this may be due to the restriction of using the same initial egg distribution for all 3 yr of simulation. The IBM simulations indicate two main recruitment areas for the north‐east Atlantic stock of mackerel, these being Porcupine Bank and the south‐eastern Bay of Biscay. These areas correspond to areas of high juvenile catches, although the juveniles generally have a more widespread distribution than the model simulations. The best agreement between modelled data and field data for distribution (juveniles and model survivors) is for the year 1998. The juvenile catches in different representative nursery areas are totalled to give a field abundance index (FAI). This index is compared with a model survivor index (MSI) which is calculated from the total of survivors for the whole spawning season. The MSI compares favourably with the FAI for 1998 and 1999 but not for 2000; in this year, juvenile catches dropped sharply compared with the previous years but there was no equivalent drop in modelled survivors.     

Dispersal of Eastern King Prawn larvae in a western boundary current: New insights from particle tracking

Patterns in larval transport of coastal species have important implications for species connectivity, conservation, and fisheries, especially in the vicinity of a strengthening boundary current. An Ocean General Circulation Model for the Earth Simulator particle tracking model was used to assess the potential dispersal of Eastern King Prawn (EKP) larvae Melicertus (Penaeus) plebejus, an important commercial and recreational species in Eastern Australia. Particles were exposed to a constant natural mortality rate, and temperature‐dependent growth (degree‐days) was used to determine the time of settlement. Forward and backward simulations were used to identify the extent of larval dispersal from key source locations, and to determine the putative spawning regions for four settlement sites. The mean dispersal distance for larvae was extensive (~750–1,000 km before settlement), yet the northern spawning locations were unlikely to contribute larvae to the most southern extent of the EKP range. There was generally great offshore dispersal of larvae, with only 2%–5% of larvae on the continental shelf at the time of settlement. Our particle tracking results were combined with existing site‐specific reproductive potentials to identify the relative contributions of larvae from key source locations. Although mid‐latitude sites had only moderate reproductive potential, they delivered the most particles to the southern coast and are probably the most important sources of larval EKP for the two southern estuaries. Our modelling suggests that mesoscale oceanography is a strong determinant of recruitment success of the EKP, and highlights the importance of both larval dispersal and reproductive potential for understanding connectivity across a species’ range.     

A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan

We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978–93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5–25 mm in standard length) is the key factor in determining the year‐class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988–93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year‐class strength during that period.     

Vertical distribution of larval Atlantic menhaden (Brevoortia tyrannus) and Atlantic croaker (Micropogonias undulatus): Implications for vertical migratory behaviour and transport

Understanding the interactions among biological and physical processes is essential to determining how the environment affects transport and survival of fishes. We examined vertical distribution in larval Atlantic menhaden (Brevoortia tyrannus) and Atlantic croaker (Micropogonias undulatus) using 126 depth stratified tows in Delaware Bay, USA, during two cruises, in December 2007 and February 2008. Menhaden larvae were 16.8–24.6 and 20.5–26.2 mm standard length in December and February. Corresponding lengths for croaker were 9.3–17.9 and 8.6–19.6 mm. Using empirical observations, and statistically derived models, we explored larval concentration for both species as a function of location, depth, diel period, tidal period, size, and pairwise interactions. Menhaden concentration was best modeled as a function of station, cruise, and interactions between depth and size as well as between station and cruise. No significant differences in larval menhaden concentration were present among tidal and diel periods. Croaker concentration was best modeled as a function of size and interactions between station and diel period, depth and size, cruise and size. Despite tidal period not emerging as a significant model parameter, we observed larger croaker larvae during nighttime flood tides. Our statistical models are consistent with processes of up‐estuary transport for both species, suggesting larvae are increasingly affected by behavioral responses as larvae grow, exhibiting stronger patterns in vertical distribution. The results refine our understanding of the potential importance of size‐related differences in vertical distribution for larval transport in these species. Future research should examine the interactions among size‐specific vertical migratory capabilities, vertical distribution, transport, and retention.     

Lipids in eggs from first-time and repeat spawning Atlantic halibut, Hippoglossus hippoglossus (L.)

Abstract The production of viable larvae is critical to any aquaculture venture. Since lipids are important components of fish eggs, the amount and nature of the lipid may be crucial to the survival of the larvae. In this study the lipid content of unfertilized eggs from first-time and repeat spawning Atlantic halibut females was compared. The egg lipid content for the first-time spawner ranged from 0·18 to 0·41mg/egg; the range for the repeat spawner was 0·27 to 0·38mg/egg. However, the mean total lipid per egg values were similar for both fish at ca. 0·31mg/egg. The repeat spawner prodticed more eggs than the first-time spawner, thus allocating more lipid to egg production. In the eggs from the two fish 62–84% of the lipids was phospholipid.     

Production, Quality, and Low Temperature Incubation of Eggs of Atlantic Cod Gadus morhua and Haddock Melanogrammus aeglefinus in Captivity

Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus broodstock maintained under altered regimens of temperature and photoperiod spawned up to 8 mo per year. The cod broodstock produced viable embryos from October through June. The haddock broodstock produced viable embryos from December through May. Egg diameters were largest during the middle of the spawning season when water temperature was at a minimum, resulting in an inverse relationship between egg diameter and water temperature in both species. Egg quality was high, as evaluated by buoyancy, fertilization rate, regularity of early cleavage, and percent viable hatch. Low temperature incubation of cod and haddock eggs extended the embryonic period. Cod embryos tolerated a wider range of temperatures than haddock. High mortality (1 90%) was observed before hatching in haddock embryos incubated at 1 C. Atlantic cod embryos hatched at temperatures as low as —1 C, extending the embryonic period to 59 d. At 8 C Atlantic cod and haddock embryos hatched in 11–12 d. To determine if extending the embryo incubation time by using low temperatures had a detrimental effect, embryos were incubated through hatch at either 1 C or 6 C, and the larvae from both groups reared at 6 C. Growth and early survival of larvae were comparable in both treatments.     

Entrainment and advection of larval sardine,Sardinops sagax,by the East Australian Current and retention in the western Tasman Front

The poleward flowing East Australian Current (EAC) drives sporadic upwelling, entrains coastal water and forms the western Tasman Front (wTF), creating a mosaic of water types and larval transport routes along south eastern Australia. The spatial distribution, otolith chemistry and growth rates of larval sardine (Sardinops sagax) were examined to infer spawning location and larval transport. A gradient of increasing larval size from north to south along the shelf was not detected but was evident between the shelf and offshore in the wTF. Here larvae were larger and older. Based on the occurrence of newly hatched larvae, spawning by S. sagax between southern Queensland and mid New South Wales (NSW) was more extensive than previously reported. The otolith chemistry from two wTF larval size classes differed, implying different origins. The otolith chemistry of wTF post‐flexion larvae was similar to larvae from northern NSW, whereas wTF flexion larvae were similar to larvae observed nearby from mid‐NSW. Two possible larval transport routes, direct and indirect, are inferred from otolith chemistry, current velocities and a previously published particle tracking study. Either larvae from northern NSW were advected south and entrained with younger larvae directly into the wTF, or larvae from a range of shelf regions were advected around the southern edge of an anticyclonic eddy, to join younger larvae directly entrained into the wTF. Based on the co‐occurrence of larval ages and sizes in the wTF and their advection routes, the wTF appears to be an important larval retention zone.