Development of an Argopecten-Specific 18S rRNA Targeted Genetic Probe

Comparison of 18S ribosomal RNA gene sequences between diverse bivalve species, including eight scallop species, allowed the design of an 18S rRNA targeted oligonucleotide probe (BS-1364) that was specific for scallops belonging to the genus Argopecten (bay and calico scallops). The high sequence similarity of the 18S rRNA gene between Argopecten irradians and Argopecten gibbus (98.8%) prevented the design of an A. irradians species-specific probe. Hybridization studies using amplified 18S rDNA from a diverse collection of bivalve species demonstrated that the specificity of the digoxygenin-labeled probe was consistent with the predicted specificity indicated by sequence comparison. Hybridization studies using laboratory-spawned bay scallop veligers indicated that a single veliger could be detected by probe hybridization in a blot format, and that probe hybridization signal was proportional (r ²= .99) to the abundance of veligers. Methods for rRNA extraction and blotting were developed that allowed bay scallop veligers to be specifically and quantitatively identified in natural plankton samples. Preliminary studies conducted in Tampa Bay, Florida, suggest that introduced scallops can successfully spawn and produce veligers under in situ conditions. The Argopecten-specific probe and methods developed in this study provide the means to study the production and fate of bay scallop larvae in nature and provide evidence that scallops introduced into Tampa Bay have the potential for successful reproduction and enhancement of scallop stocks. Received January 25, 1999; accepted May 7, 1999.     

Importance of the upper estuary as a nursery ground for fishes in Ariake Bay,Japan

To examine the importance of the upper estuarine areas of Ariake Bay as a nursery ground for fish, assemblages of larvae and juveniles were compared among various aquatic habitats. The upper estuaries of the bay (the Rokkaku and Hayatsue estuaries) are brackish, highly turbid waters with high tidal velocities, and differ substantially from the Isahaya area, which has been separated from the bay by a man-made dike, to the middle estuary (the Kikuchi estuary). Abundances of larvae and juveniles were higher in the estuaries than in the open bay and Isahaya areas. Abundant species in the upper estuaries were similar to each other, but differed from those of the middle estuary. This was primarily due to larvae and juveniles of fishes that occurred almost entirely in the upper estuaries, such as Acanthogobius hasta, Boleophthalmus pectinirostris, Coilia nasus, Cynoglossus abbreviatus, Nibea albiflora, Odontamblyopus lacepedii, Trachidermus fasciatus and Tridentiger barbatus. These results suggest that the upper estuaries play an important role as nursery grounds for fishes.     

Using molecular pedigree reconstruction to evaluate the long-term survival of outplanted hatchery-reared larval and juvenile northern abalone (<Emphasis Type="Italic">Haliotis kamtschatkana</Emphasis>)

The restoration of abalone (Haliotis spp.) populations through supplementation with the offspring of hatchery-spawned wild parents has been attempted in several species, with variable results. Between 2002 and 2005, the Bamfield Huu-ay-aht Community Abalone Project released 4.5 million larvae and 152,000 juveniles of the northern abalone (Haliotis kamtschatkana) into Barkley Sound, BC. The purpose of this study was to estimate the long-term survival of outplanted abalone 3–7 years after their release and thus determine their contribution to local population densities at three different outplanting sites. We identified outplanted abalone by genotyping epipodal tentacles sampled from wild-caught abalone for seven microsatellite loci. We then used three different pedigree reconstruction programs: one that used genotypes from hatchery-reared siblings (pedigree 2.2), one that used the wild parent genotypes that were available (cervus 3.0), and one that used both sources of information (colony 2.0). Each program identified different but partially overlapping subsets of hatchery-outplanted offspring. From this we inferred that up to 26% of the individuals sampled at the main outplanting site were from hatchery spawnings. Despite this large contribution of hatchery-reared stock, the density of mature abalone at each site was below the level required for successful fertilization. More intensive outplanting efforts might increase population densities of this broadcast spawner above this minimum sustainable level. However, for supplementation to be successful, other factors that could reduce outplanted juvenile survival, including the low genetic diversity of hatchery-produced offspring and the low habitat quality of some outplanting sites, need to be monitored.     

THE EFFECT OF SEAWEED DIETS ON GROWTH OF GREEN ABALONE,HALIOTIS FULGENS,FROM BAJA CALIFORNIA,MEXICO

Two abalone species: green Haliotis fulgens and yellow Halioti corrugata represent nearly 97% of the total production in the Mexican abalone fishery. It has been assumed that abalone feed on the kelp algae Macrocystis pyrifera. Regional hatcheries use this species as a main source of natural food. M. pyrifera does not occur at the southern limit of the distribution of abalone species along the Baja California Peninsula. In this study, growth rates of juveniles H. fulgens, 17.3 ± 2.2 mm shell length and 0.4 ± 0.2 g body weight, were evaluated. Juveniles were fed with common species in the benthic environments inhabited by abalone along the western coast of Baja California during 191 days. Three diets were based on algae: palm kelp, Eisenia arborea, giant kelp, M. pyrifera and Gelidium robustum, and one on seagrass, Phyllospadix torreyi. Shell length and body growth rates varied between 21.5 μm day^?1 and 2.2 mg day^?1 for E. arborea and between 45.9 μm day^?1 and 6.7 mg day^?1 for M. pyrifera. Higher specific growth rates (SGR) in length and weight were determined for M. pyrifera: 0.2% and 0.7% day^?1. Significant differences between values of juveniles fed M. pyrifera with the rest of the diets were found. The highest mortality (21%) was in juveniles fed the red algae G. robustum.     

Development and Linkage Analysis of 104 New Microsatellite Markers for Bay Scallop (Argopecten irradians)

For genetic analysis and linkage mapping of bay scallop (Argopecten irradians), a set of 120 novel simple sequence repeat markers were developed from microsatellite-enriched libraries and expressed sequence tags. An inter-subspecies hybrid bay scallop family (CC5) of 46 progeny was analyzed as the reference population to confirm polymorphism and test the segregation patterns of these loci. A total of 104 microsatellite markers were polymorphic in the reference family, among which 36 in female, 28 in male, and 40 in both parents, respectively. Linkage analysis allowed mapping these markers to 15 linkage groups, which is close to the haploid chromosome number of bay scallop (n = 16). Analysis of the 40 markers segregating in both parents showed a higher recombination rate in the female parent, with the average of female-to-male recombination ratio of 1.09:1 between linked pairs of markers. When null alleles were considered, there were 17 loci showing segregation distortion at the 5% significance level using the chi-square test. The microsatellite markers developed in this study provide a useful resource for future linkage mapping and quantitative loci analysis in A. irradians.     

The early life history of kurosoi,Sebastes schlegeli (Scorpaenidae), in the Sea of Japan

Larval and juvenile stages of kurosoi,Sebastes schlegeli, are described and illustrated from wild specimens. Some ecological aspects of larvae and juveniles are also described. Notochord flexion occurred between 5.6–7.5 mm SL. Transformation occurred between 13–20 mm SL. Preflexion and flexion larvae ofS. schlegeli can be distinguished from similar larvae by the pigmentation of the dorsal and ventral midlines of the tail and absence of pigmentation on the ventral portion of the rectum. After notochord flexion, the dorsal and lateral regions in both larvae and pelagic juveniles were heavily pigmented, suggesting adaptation for neustonic life style. Larvae and juveniles were caught at many coastal stations, but did not occur in cooler offshore waters. Larvae smaller than 20 mm SL inhabited surface waters. Until ca. 40 mm SL, juveniles inhabited mainly surface waters (without drifting seaweed), but also used other habitats, such as the drifting seaweed, and near the sea bed. Small larvae (<7 mm SL) fed mainly on copepod nauplii. Larger larvae fed on calanoid copepodites andEvadne nordmanni. Pelagic juveniles fed mainly on fish eggs, with fish larvae also being important food items for some individuals. Most food items taken by juveniles that were associated with drifting seaweed were eggs with attaching filaments (Cololabis saira andHyporhamphus sajori), suggesting that the high density of such food items both attracts and keeps juveniles around drifting seaweed.     

The manganese superoxide dismutase gene in bay scallop Argopecten irradians: cloning, 3D modelling and mRNA expression

A novel manganese superoxide dismutase (MnSOD) was cloned from bay scallop Argopecten irradians by 3' and 5' rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA of MnSOD was of 1207bp with a 678bp open reading frame encoding 226 amino acids. The deduced amino acid sequence contained a putative signal peptide of 26 amino acids. Sequence comparison showed that the MnSOD of A. irradians shared high identity with MnSOD in invertebrates and vertebrates, such as MnSOD from abalone Haliotis discus discus (ABG88843) and frog Xenopus laevis (AAQ63483). Furthermore, the 3D structure of bay scallop MnSOD was predicted by SWISS-MODEL Protein Modelling Server and compared with those of other MnSODs. The overall structure of bay scallop MnSOD was similar to those of zebrafish Danio rerio, fruit fly Drosophila melanogaster, Chinese shrimp Fenneropenaeus chinensis, human Homo sapiens, and had the highest similarity to scallop Mizuhopecten yessoensis and abalone H. discus discus. A quantitative real-time PCR (qRT-PCR) assay was developed to detect the mRNA expression of MnSOD in different tissues and the temporal expression in haemocytes following challenge with the bacterium Vibrio anguillarum. A higher-level of mRNA expression of MnSOD was detected in gill and mantle. The expression of MnSOD reached the highest level at 3h post-injection with V. anguillarum and then slightly recovered from 6 to 48h. The results indicated that bay scallop MnSOD was a constitutive and inducible protein and thus could play an important role in the immune responses against V. anguillarum infection.     

Spatiotemporal occurrence and feeding habits of tonguefish,Cynoglossus lighti Norman, 1925, larvae in Ariake Bay,Japan

Spatiotemporal occurrence and feeding habits of tonguefish (Cynoglossus lighti Norman, 1925) larvae were investigated in an offshore area (>5 m in depth) of the inner part of Ariake Bay, Japan. All specimens were symmetric, free‐swimming larvae. Although their seasonal abundance and distribution in the study site varied from year to year, spawning started in June and the larval abundance was high in August and September with a wide distribution in the inner part of the bay. Both present and previous study results strongly suggest that larvae may settle primarily in the estuary and near‐shore areas of Ariake Bay after their wide distribution in the offshore area of the bay during the free‐swimming stage. Larvae showed a clear feeding rhythm in which they fed on prey mainly during the daytime. Larvae fed exclusively on copepods, and identified prey were mostly Paracalanidae (mainly Parvocalanus crassirostris), Microsetella norvegica, and Oithona davisae. Pre‐metamorphosis larvae fed primarily on Paracalanidae and O. davisae, whereas O. davisae formed a smaller proportion of the early‐metamorphosis diet. In early metamorphoses, larvae fed preferentially on Paracalanidae and M. norvegica.     

Comparison of growth and lipid composition in the green abalone, Haliotis fulgens, provided specific macroalgal diets

Lipid composition of abalone was examined over a one-year interval. A feeding trial was designed to cover a full reproductive cycle in young adult green abalone, Haliotis fulgens, consisting of five diet treatments: the macrophytic algal phaeophyte Egregia menziesii, rhodophyte Chondracanthus canaliculatus, chlorophyte Ulva lobata, a composite of the three algae and a starvation control. The lipid class, fatty acid, sterol and 1-O-alkyl glyceryl ether profiles were determined for foot, hepatopancreas/gonad tissues and larvae. The major fatty acids were 16:0, 18:0, 18:1(n-7)c, 18:1(n-9)c, 20:4(n-6), 20:5(n-3) and 22:5(n-3), as well as 14:0 for abalone fed brown and red algae. 4,8,12-Trimethyltridecanoic acid, derived from algae, was detected for the first time in H. fulgens (hepatopancreas complex, 1.2–13.9%; larvae, 0.5% of total fatty acids). Diacylglyceryl ethers were present in larvae (0.6% of total lipid). The major 1-O-alkyl glycerols were 16:0, 16:1 and 18:0. Additionally, 18:1(n-9) was a major component in hepatopancreas/gonad and larvae. The major sterol was cholesterol (96–100% of total sterols). Highest growth rates were linked to temperature and occurred in abalone fed the phaeophyte E. menziesii (43 μm·day^–1, 56 mg·day^–1 yearly mean), an alga containing the highest levels of C₂₀ polyunsaturated fatty acids and the highest ratio of 20:4(n-6) to 20:5(n-3). This study provides evidence of the influence of diet and temperature on seasonal changes in abalone lipid profiles, where diet is most strongly related to body mass and temperature to shell length. The allocation of lipids to specific tissues in green abalone clarifies their lipid metabolism. These results provide a basis for improving nutrition of abalone in mariculture through formulation of artificial feeds.     

Empirical evidence for large‐scale human impact on intertidal aggregations,larval supply and recruitment of Pyura praeputialis around the Bay of Antofagasta,Chile

In northern Chile, Pyura praeputialis is an invasive species inhabiting rocky intertidal and subtidal habitats restricted exclusively to the Bay of Antofagasta where it forms extensive aggregations. The negative impact of Pyura gathering on mid‐intertidal abundances of this species has recently been reported at the south‐eastern end of this bay. In the present study we have increased sampling sites to cover the entire bay toward the north‐western end and the northern section, where a coastal marine reserve for the scallop fishery partially restricts shellfish gathering. Therefore, the sampling sites were chosen to represent different levels of shellfish gathering access along the northern shore of the bay. Long‐term monitoring (1999–2014) of changes in tunicate cover and the abundances of larvae and recruits at seven sites are reported. The opening of a remodelled artificial and recreational beach in 2012, on the central‐eastern shore of the bay, has increased accessibility to rocky intertidal platforms that started to be massively visited by Pyura gatherers from the summer of 2013. This allowed for the implementation of an intensive short‐term monitoring program of changes in tunicate cover and the abundances of their larvae and recruits. When gathering access was present the reduction in intertidal cover was generalized to the entire bay and followed by reductions in larvae and recruits. However, these reductions were not found in sites with more restricted gathering access. We conclude that continuous extraction by Pyura gatherers followed by reductions of conspecific larvae and recruits are the main drivers behind the reduced abundance of P. praeputialis in the entire bay of Antofagasta. Thus, if gathering is not stopped important ecosystem services provided by this tunicate in the bay may be threatened. Similar consequences may be expected if other massive and irreversible reductions in other species of the Pyura complex, that inhabit other coasts in the southern hemisphere, occur. The controversy concerning the impacts of invasive species and whether they cause negative, positive or neutral impacts to original ecosystems and fisheries is discussed.     

Molecular Studies on the Microbial Diversity Associated with Mining-Impacted Coeur d’Alene River Sediments

Mass mortalities of larval cultures of Chilean scallop Argopecten purpuratus have repeatedly occurred in northern Chile, characterized by larval agglutination and accumulation in the bottom of rearing tanks. The exopolysaccharide slime (EPS) producing CAM2 strain was isolated as the primary organism from moribund larvae in a pathogenic outbreak occurring in a commercial hatchery producing larvae of the Chilean scallop Argopecten purpuratus located in Bahía Inglesa, Chile. The CAM2 strain was characterized biochemically and was identified by polymerase chain reaction amplification of 16S rRNA as Halomonas sp. (Accession number DQ885389.1). Healthy 7-day-old scallop larvae cultures were experimentally infected for a 48-h period with an overnight culture of the CAM2 strain at a final concentration of ca. 10⁵ cells per milliliter, and the mortality and vital condition of larvae were determined by optical and scanning electron microscopy (SEM) to describe the chronology of the disease. Pathogenic action of the CAM2 strain was clearly evidenced by SEM analysis, showing a high ability to adhere and detach larvae velum cells by using its “slimy” EPS, producing agglutination, loss of motility, and a posterior sinking of scallop larvae. After 48 h, a dense bacterial slime on the shell surface was observed, producing high percentages of larval agglutination (63.28 ± 7.87%) and mortality (45.03 ± 4.32%) that were significantly (P < 0.05) higher than those of the unchallenged control cultures, which exhibited only 3.20 ± 1.40% dead larvae and no larval agglutination. Furthermore, the CAM2 strain exhibited a high ability to adhere to fiberglass pieces of tanks used for scallop larvae rearing (1.64 × 10⁵ cells adhered per square millimeters at 24 h postinoculation), making it very difficult to eradicate it from the culture systems. This is the first report of a pathogenic activity on scallop larvae of Halomonas species, and it prompts the necessity of an appraisal on biofilm-producing bacteria in Chilean scallop hatcheries.     

A Consensus Microsatellite-Based Linkage Map for the Hermaphroditic Bay Scallop (Argopecten irradians) and Its Application in Size-Related QTL Analysis

Bay scallop (Argopecten irradians) is one of the most economically important aquaculture species in China. In this study, we constructed a consensus microsatellite-based genetic linkage map with a mapping panel containing two hybrid backcross-like families involving two subspecies of bay scallop, A. i. irradians and A. i. concentricus. One hundred sixty-one microsatellite and one phenotypic (shell color) markers were mapped to 16 linkage groups (LGs), which corresponds to the haploid chromosome number of bay scallop. The sex-specific map was 779.2 cM and 781.6 cM long in female and male, respectively, whereas the sex-averaged map spanned 849.3 cM. The average resolution of integrated map was 5.9 cM/locus and the estimated coverage was 81.3%. The proportion of distorted markers occurred more in the hybrid parents, suggesting that the segregation distortion was possibly resulted from heterospecific interaction between genomes of two subspecies of bay scallop. The overall female-to-male recombination rate was 1.13∶1 across all linked markers in common to both parents, and considerable differences in recombination also existed among different parents in both families. Four size-related traits, including shell length (SL), shell height (SH), shell width (SW) and total weight (TW) were measured for quantitative trait loci (QTL) analysis. Three significant and six suggestive QTL were detected on five LGs. Among the three significant QTL, two (qSW-10 and qTW-10, controlling SW and TW, respectively) were mapped on the same region near marker AiAD121 on LG10 and explained 20.5% and 27.7% of the phenotypic variance, while the third (qSH-7, controlling SH) was located on LG7 and accounted for 15.8% of the phenotypic variance. Six suggestive QTL were detected on four different LGs. The linkage map and size-related QTL obtained in this study may facilitate marker-assisted selection (MAS) in bay scallop.     

Microsatellite Genotyping of Individual Abalone Larvae: Parentage Assignment in Aquaculture

In aquaculture, microsatellite DNA markers are used to genotype parental broodstock, to assess fertilization success, and to maintain pedigree information for selective breeding. In this study we genotyped individual Haliotis asinina larvae by analyzing a suit of polymorphic microsatellite loci. At least 10 loci can be analyzed from a single abalone veliger larva. We assayed 5 polymorphic loci to identify the parents of individual larvae produced in 3 separate crosses. In all cases, the parents of an individual veliger could be determined from as few as 3 loci. The microsatellite analysis revealed that, in each of our crosses, a single male fathered most of the veligers, despite efforts to normalize the amount of sperm contributed by competing males. These observations suggest that highly controlled breeding practices may be required to ensure that the genetic diversity of an abalone population produced for aquaculture is maintained at the level of diversity of the original broodstock. Received December 4, 2000; accepted May 22, 2001.     

Early development and occurrence patterns of the Pagrinae seabream Argyrops bleekeri (Perciformes: Sparidae): Does early life history have implications for sparid relationships?

The early development and occurrence patterns of Argyrops bleekeri are described based on 87 specimens collected from Nakagusuku Bay on Okinawa Island in southwestern Japan. Larvae and juveniles of the genus Argyrops are distinguished from the other seabreams inhabiting the Western Pacific region by the strength and extent of head spination, body depth, dorsal-fin-ray counts and melanophore patterns. Argyrops bleekeri is easily distinguished from other members of this genus by the presence of a single rudimentary dorsal-fin spine on the first dorsal pterygiophore, melanophore patterns and an allopatric distribution. Argyrops bleekeri larvae [3.3–7.1 mm body length (BL)] and juveniles (6.7–13.0 mm BL) were found in the bay from January to May; nonetheless, they were not collected from the outer bay or in extremely shallow inshore areas such as tidal flats. The results suggest that Argyrops is the most derived red seabream because of its spiny morphology, and it may be a member of an expanding nearshore group of red seabreams, which originally inhabited offshore waters.     

The potential threat of algal blooms to the abalone (Haliotis midae) mariculture industry situated around the South African coast

Toxic algal blooms are common world-wide and pose a serious problem to the aquaculture and fishing industries. Dinoflagellate species such as Karenia brevis, Karenia mikimotoi, Heterosigma akashiwo and Chatonella cf. antiqua are recognised toxic species implicated in various faunal mortalities. Toxic blooms of Karenia cristata were observed on the south coast of South Africa for the first time in 1988 and were responsible for mortalities of wild and farmed abalone. K. cristata and various other dinoflagellate species common along the South African coast, as well as K. mikimotoi (Isolation site: Norway, Univ. of Copenhagen) and K. brevis (Isolation site: Florida, BIGELOW), were tested for toxicity by means of a bioassay involving Artemia larvae as well as abalone larvae and spat. K. cristata, like K. brevis, contains an aerosol toxin; however, the toxin present in K. cristata has not yet been isolated and remains unknown. K. brevis was, therefore, used to determine which developmental phase of the bloom would affect abalone farms most, and whether ozone could be used as an effective mitigating agent. Of the 17 dinoflagellate species tested, K. cristata, Akashiwo sanguinea, K. mikimotoi and K. brevis pose the greatest threat to the abalone mariculture industry. K. brevis was most toxic during its exponential and stationary phases. Results suggest that ozone is an effective mitigation agent but its economic viability for use on abalone farms must still be investigated.     

Effect of eight benthic diatoms as feed on the growth of red abalone (Haliotis rufescens) postlarvae

The growth rate of abalone post larvae of Haliotis rufescens fed ad libitum with a benthic monoalgal diatom culture maintained as monocultures on a semi-commercial scale, was evaluated and correlated with the biochemical composition of the diatoms. The cell size (7.0 × 4.0 μm to 21.0 × 7.5 μm), protein percentage (7.42% to 13.66%), and ash content (49.03% to 59.61%) were different among diatom strains; lipid percentage, nitrogen free extract, and energy content (Kcal g⁻¹) were similar among diatom strains. The values of essential and non-essential amino and fatty acids composition differed among diatom strains. Differences in the abalone shell length and orthogonal analyses revealed postlarval growth was dependent on the quality of the food source. Postlarvae abalone displaying the longest shell lengths were fed Nitzschia thermalis var. minor and Amphiprora paludosa var. hyalina (1,712.0 ± 61 μm and 1,709 ± 67 μm, respectively), followed by Navicula incerta (1,413.3 ± 43 μm). The fatty acid content of benthic diatoms and abalone growth rate were not correlated.     

Colonization of the Gastrointestinal Tract of the Farmed South African Abalone Haliotis midae by the Probionts Vibrio midae SY9, Cryptococcus sp. SS1, and Debaryomyces hansenii AY1

Viable cell counts and/or in situ hybridization were used to determine whether the probionts Vibrio midae SY9, Cryptococcus sp. SS1, and Debaryomyces hansenii AY1 can colonize the gastrointestinal tract of the South African abalone Haliotis midae. The number of culturable probiotic cells reisolated from H. midae fed probiotic-supplemented feed for 3 weeks ranged from 10⁶ to 10⁷ cfu/g gut material. A significant decrease (P < 0.05) in probiont numbers 2 days after feeding the probiotic-supplemented feed had been halted correlated with a significant decrease (P < 0.05) in intestinal protease and amylase activity. There was a positive correlation between Cryptococcus sp. SS1 and amylase activity (r² = 0.681) and V. midae SY9.8 and protease activity (r² = 0.711) in the H. midae intestine. Although culturable probionts were isolated from abalone that had not been fed probiotic-supplemented feed for a 2-week period, the drop in the number of probiotic cells colonizing the abalone digestive tract 2 days after feeding with the probiotic-supplemented feed had been halted indicates that farmed abalone should be fed probiotic-supplemented feed at least every second day for maximum benefit.     

Utilisation of a tropical bay as a nursery area by sharks of the families Carcharhinidae and Sphyrnidae

Synopsis At least eight species of sharks of the families Carcharhinidae and Sphyrnidae use Cleveland Bay in northern Australia as a communal nursery area.Carcharhinus dussumieri, C. fitzroyensis, C. limbatus andC. tilstoni use the bay as a seasonal primary nursery, with juveniles occurring in it for only a few months each year immediately after birth. Alternatively,Carcharhinus sorrah, Rhizoprionodon acutus andR. taylori use the bay as a year-round primary and secondary nursery, with juveniles remaining in it up to the size at maturity. AdultR. taylori also persist in the bay, a behavioural pattern possibly explained by their small maximum size. While present immediately after birth the type of utilisation pattern displayed bySphyrna lewini could not be clarified in this study. Although diets of these species in the bay are similar, there is probably little direct competition for food due to the highly productive habitats in the bay supporting an abundance of food resources. The highest numbers of juveniles occur when prey species are the most abundant, and when temporal separation of some seasonally-occurring species of sharks in effect.