Sex-specific growth and mortality, spawning season, and female maturation of the stripey bass (Lutjanus carponotatus) on the Great Barrrier Reef

Sex-specific demography and reproductive biology of stripey bass (Lutjanus carponotatus) (also known as Spanish flag snapper, FAO) were examined at the Palm and Lizard island groups, Great Barrier Reef (GBR).Total mortality rates were similar between the sexes. Males had larger L∞ at both island groups and Lizard Island group fish had larger overall L∞. Female:male sex ratios were 1.3 and 1.1 at the Palm and Lizard island groups, respectively. The former is statistically different from 1, but is unlikely significantly different in a biological sense. Females matured on average at 2 years of age and 190 mm fork length at both locations. Female gonadal lipid body indices peaked from August through October, preceding peak gonadosomatic indices in October, November, and December that were twice as great as in any other month. However, ovarian staging revealed 50% or more ovaries were ripe from September through February, suggesting a more protracted spawning season and highlighting the different interpretations that can arise between gonad weight and gonad staging methods. Gonadosomatic index increases slightly with body size and larger fish have a longer average spawning season, which suggests that larger fish produce greater relative reproductive output. Lizard Island group females had ovaries nearly twice as large as Palm Island group females at a given body size. However, it is unclear whether this reflects spatial differences akin to those observed in growth or effects of sampling Lizard Island group fish closer to their date of spawning. These results support an existing 250 mm minimum size limit for L. carponotatus on the GBR, as well as the timing of a proposed October through December spawning closure for the fishery. The results also caution against assessing reef-fish stocks without reference to sex-, size-, and location-specific biological traits.

Individual growth rates and movement of juvenile white shrimp (Litopenaeus setiferus) in a tidal marsh nursery

We measured growth and movements of individually marked free-ranging juvenile white shrimp (Litopenaeus setiferus) in tidal creek subsystems of the Duplin River, Sapelo Island, Georgia. Over a period of two years, 15,974 juvenile shrimp (40−80 mm TL) were marked internally with uniquely coded microwire tags and released in the shallow upper reaches of four salt marsh tidal creeks. Subsequent samples were taken every 3−6 days from channel segments arranged at 200-m intervals along transects extending from the upper to lower reach of each tidal creek. These collections included 201,384 juvenile shrimp, of which 184 were marked recaptures. Recaptured shrimp were at large an average of 3−4 weeks (range: 2−99 days) and were recovered a mean distance of <0.4 km from where they were initially marked. Mean residence times in the creek subsystems ranged from 15.2 to 25.5 days and were estimated from exponential decay functions describing the proportions of marked individuals recaptured with increasing days at large. Residence time was not significantly correlated with creek length (Pearson=−0.316, P=0.684 ), but there was suggestive evidence of positive associations with either intertidal (Pearson r=0.867, P=0.133) or subtidal (Pearson r=0.946, P=0.054) drainage area. Daily mean specific growth rates averaged 0.009 to 0.013 among creeks; mean absolute growth rates ranged from 0.56−0.84 mm/d, and were lower than those previously reported for juvenile penaeids in estuaries of the southeastern United States. Mean individual growth rates were not significantly different between years (t-test, P>0.30) but varied significantly during the season, tending to be greater in July than November. Growth rates were size-dependent, and temporal changes in size distributions rather than temporal variation in physical environmental factors may have accounted for seasonal differences in growth. Growth rates differed between creeks in 1999 (t-test, P<0.015), but not in 1998 (t-test, P>0.5). We suggest that spatial variation in landscape structure associated with access to intertidal resources may have accounted for this apparent interannual difference in growth response.

Maturity, ovarian cycle, fecundity, and age-specific parturition of black rockfish (Sebastes melanops)

From 1995 to 1998, we collected female black rockfish (Sebastes melanops) off Oregon in order to describe their basic reproductive life history and determine age-specific fecundity and temporal patterns in parturition. Female black rockfish had a 50% probability of being mature at 394 mm fork length and 7.5 years-of-age. The proportion of mature fish age 10 or older significantly decreased each year of this study, from 0.511 in 1996 to 0.145 in 1998. Parturition occurred between mid-January and mid-March, and peaked in February. We observed a trend of older females extruding larvae earlier in the spawning season and of younger fish primarily responsible for larval production during the later part of the season. There were differences in absolute fecundity at age between female black rockfish with prefertilization oocytes and female black rockfish with fertilized eggs; fertilized-egg fecundity estimates were considered superior. The likelihood of yolked oocytes reaching the developing embryo stage increased with maternal age. Absolute fecundity estimates (based on fertilized eggs) ranged from 299,302 embryos for a 6-year-old female to 948,152 embryos for a 16-year-old female. Relative fecundity (based on fertilized eggs) increased with age from 374 eggs/g for fish age 6 to 549 eggs/g for fish age 16.

Dynamics of bigeye (Thunnus obesus) and yellowfin (T. albacares) tuna in Hawaii’s pelagic fisheries: analysis of tagging data with a bulk transfer model incorporating size-specific attrition

Tag release and recapture data of bigeye (Thunnus obesus) and yellowfin tuna (T. albacares) from the Hawaii Tuna Tagging Project (HTTP) were analyzed with a bulk transfer model incorporating size-specific attrition to infer population dynamics and transfer rates between various fishery components. For both species, the transfer rate estimates from the offshore handline fishery areas to the longline fishery area were higher than the estimates of transfer from those same areas into the inshore fishery areas. Natural and fishing mortality rates were estimated over three size classes: yellowfin 20–45, 46–55, and ≥56 cm and bigeye 29–55, 56–70, and ≥71 cm. For both species, the estimates of natural mortality were highest in the smallest size class. For bigeye tuna, the estimates decreased with increasing size and for yellowfin tuna there was a slight increase in the largest size class. In the Cross Seamount fishery, the fishing mortality rate of bigeye tuna was similar for all three size classes and represented roughly 12% of the gross attrition rate (includes fishing and natural mortality and emigration rates). For yellowfin tuna, fishing mortality ranged between 7% and 30%, the highest being in the medium size class. For both species, the overall attrition rate from the entire fishery area was nearly the same. However, in the specific case of the Cross Seamount fishery, the attrition rate for yellowfin tuna was roughly twice that for bigeye. This result indicates that bigeye tuna are more resident at the Seamount than yellowfin tuna, and larger bigeye tunas tend to reside longer than smaller individuals. This may result in larger fish being more vulnerable to capture in the Seamount fishery. The relatively low level of exchange between the Sea-mount and the inshore and longline fisheries suggests that the fishing activity at the Seamount need not be of great management concern for either species. However, given that the current exploitation rates are considered moderate (10–30%), and that Seamount aggregations of yellowfin and bigeye tuna are highly vulnerable to low-cost gear types, it is recommended that further increases in fishing effort for these species be monitored at Cross Seamount.

Shortspine thornyhead (Sebastolobus alascanus) abundance and habitat associations in the Gulf of Alaska

Shortspine thornyhead (Sebastolobus alascanus) abundance was estimated from 107 video transects at 27 stations recorded from a research submersible in 1991 off southeast Alaska at depths ranging from 165 to 355 m. Numbers of invertebrates in seven major taxa were estimated, as was substrate type. Thornyhead abundance ranged from 0 to 7.5/100 m2, with a mean of 1.22/100 m2, and was positively correlated with depth and amount of hard substrate. Invertebrate abundances were not significantly correlated with numbers of thornyheads. Shortspine thornyhead abundance estimates from this study were several times higher than estimates produced by bottom trawl surveys off southeast Alaska in 1990 and 1993, the two years of survey that encompassed the submersible transects; however, the trend of increasing abundance with depth was similar in the trawl surveys and in the submersible transects, suggesting that trawl surveys systematically underestimate abundance of shortspine thornyheads

Nuclear and mitochondrial DNA markers for specific identification of istiophorid and xiphiid billfishes

Independent molecular markers based on mitochondrial and nuclear DNA were developed to provide positive identification of istiophorid and xiphiid billfishes (marlins, spearfishes, sailfish, and swordfish). Both classes of markers were based on amplification of short segments (<1.7 kb) of DNA by the polymerase chain reaction and subsequent digestion with informative restriction endonucleases. Candidate markers were evaluated for their ability to discriminate among the different species and the level of intraspecific variation they exhibited. The selected markers require no more than two restriction digestions to allow unambiguous identification, although it was not possible to distinguish between white marlin and striped marlin with any of the genetic characters screened in our study. Individuals collected from throughout each species’ range were surveyed with the selected markers demonstrating low levels of intraspecific character variation within species. The resulting keys provide two independent means for the forensic identification of fillets and for specific identification of early life history stages.

Pacific sea surface temperature associations with southwestern United States summer rainfall and atmospheric circulation

Pacific sea surface temperatures (SSTs) are examined for their associations with (1) summer rainfall, and (2) the latitude location of the mid-tropospheric subtropical high pressure ridge (STR) in the southwestern United States during 1945 to 1986. Extreme northward (southward) displacements of STR are associated with wet (dry) summers over Arizona and an enhanced (weakened) gradient of SST off the California and Baja coasts. These tend to follow winters marked by positive (negative) phases of the PNA, Pacific/North America, teleconnection pattern. Recent decadal variations of Arizona summer rainfall (1950s wet; 1970s dry) appear similarly related to southwestern United States synoptic circulation and eastern Pacific SSTs.

Dog chromosome-specific paints reveal evolutionary inter- and intrachromosomal rearrangements in the American mink and human

Forty chromosome-specific paint probes of the domestic dog (Canis familiaris, 2n = 78) were used to delineate conserved segments on metaphase chromosomes of the American mink (Mustela vison, 2n = 30) by fluorescence in situ hybridisation. Half of the 38 canine autosomal probes each painted one pair of homologous segments in a diploid mink metaphase, whereas the other 19 dog probes each painted from two to five pairs of discrete segments. In total, 38 canine autosomal paints highlighted 71 pairs of conserved segments in the mink. These painting results allow us to establish a complete comparative chromosome map between the American mink and domestic dog. This map demonstrates that extensive chromosome rearrangements differentiate the karyotypes of the dog and American mink. The 38 dog autosomes could be reconstructed from the 14 autosomes of the American mink through at least 47 fissions, 25 chromosome fusions, and six inversions. Furthermore, comparison of the current dog/mink map with the published human/dog map discloses 23 cryptic intrachromosomal rearrangements in 10 regions of conserved synteny in the human and American mink genomes and thus further refined the human/mink comparative genome map. Copyright (C) 2000 S. Karger AG, Basel.