Spatial subdivision among assemblages of Spanish mackerel, Scomberomorus commerson (Pisces: Scombridae) across northern Australia: implications for fisheries management

Aim This study investigated the use of stable δ¹³C and δ¹⁸O isotopes in the sagittal otolith carbonate of narrow‐barred Spanish mackerel, Scomberomorus commerson, as indicators of population structure across Australia. Location Samples were collected from 25 locations extending from the lower west coast of Western Australia (30°), across northern Australian waters, and to the east coast of Australia (18°) covering a coastline length of approximately 9500 km, including samples from Indonesia. Methods The stable δ¹³C and δ¹⁸O isotopes in the sagittal otolith carbonate of S. commerson were analysed using standard mass spectrometric techniques. The isotope ratios across northern Australian subregions were subjected to an agglomerative hierarchical cluster analysis to define subregions. Isotope ratios within each of the subregions were compared to assess population structure across Australia. Results Cluster analysis separated samples into four subregions: central Western Australia, north Western Australia, northern Australia and the Gulf of Carpentaria and eastern Australia. Isotope signatures for fish from a number of sampling sites from across Australia and Indonesia were significantly different, indicating population separation. No significant differences were found in otolith isotope ratios between sampling times (no temporal variation). Main conclusions Significant differences in the isotopic signatures of S. commerson demonstrate that there is unlikely to be any substantial movement of fish among these spatially discrete adult assemblages. The lack of temporal variation among otolith isotope ratios indicates that S. commerson populations do not undergo longshore spatial shifts in distribution during their life history. The temporal persistence of spatially explicit stable isotopic signatures indicates that, at these spatial scales, the population units sampled comprise functionally distinct management units or separate ‘stocks’ for many of the purposes of fisheries management. The spatial subdivision evident among populations of S. commerson across northern and western Australia indicates that it may be advantageous to consider S. commerson population dynamics and fisheries management from a metapopulation perspective (at least at the regional level).     

Variation in stable isotope (δO and δC) signatures in the sagittal otolith carbonate of king threadfin, Polydactylus macrochir across northern Australia reveals multifaceted stock structure

Otoliths of king threadfin, Polydactylus macrochir were collected from 2007 to 2009 at nine locations across northern Australia representing most of their distributional range and areas where fisheries are active. Measurement of the stable isotope ratios of δ¹⁸O and δ¹³C in the sagittal otolith carbonate from assemblages of P. macrochir revealed location-specific signatures and indicated that adult fish sampled from representative sites across their range were significantly different. The significant differences in the isotopic signatures of P. macrochir demonstrated that population subdivision is evident and there is unlikely to be substantial movement of fish among these distinct adult assemblages. The stable isotopic signatures for the fish from the different locations were persistent through time, and therefore it could be concluded that they comprise separate stocks for many of the purposes of fisheries management. The spatial separation of these populations indicates a complex stock structure across northern Australia with stocks of P. macrochir associated with large coastal beaches and embayments on a fine spatial scale. These results indicate that in order to achieve optimal fisheries management, the current spatial management arrangements need to be reviewed, particularly the potential for localised depletion of stocks on small spatial scales. This study has provided further evidence that measurement of the stable isotopes ratios in teleost sagittal otolith carbonate can be a valuable tool in the delineation of fishable stocks or fishery management units of adult fish and that widely distributed fish can nonetheless show strong localised population structure.     

Genetic population structure of grey mackerel Scomberomorus semifasciatus in northern Australia

This study used mtDNA sequence and microsatellite markers to elucidate the population structure of Scomberomorus semifasciatus collected from 12 widespread sampling locations in Australia. Samples (n = 544) were genotyped with nine microsatellite loci, and 353 were sequenced for the control (384 bp) and ATPase (800 bp) mtDNA gene regions. Combined interpretation of microsatellite and mtDNA data identified four genetic stocks of S. semifasciatus: Western Australia, north-west coast of the Northern Territory, Gulf of Carpentaria and the eastern coast of Queensland. Connectivity among stocks across northern Australia from the Northern Territory to the eastern coast of Queensland was high (mean F(ST) = 0·003 for the microsatellite data and Φ(ST) = 0·033 and 0·009 for control region and ATPase, respectively) leading to some uncertainty about stock boundaries. In contrast, there was a clear genetic break between the stock in Western Australia compared to the rest of northern Australia (mean F(ST) = 0·132 for the microsatellite data and Φ(ST) = 0·135 and 0·188 for control region and ATPase, respectively). This indicates a restriction to gene flow possibly associated with suboptimal habitat along the Kimberley coast (north Western Australia). The appropriate scale of management for this species corresponds to the jurisdictions of the three Australian states, except that authorities in Queensland and Northern Territory should co-ordinate the management of the Gulf of Carpentaria stock.     

Distribution of sawfishes (Pristidae) in the Queensland Gulf of Carpentaria,Australia, with notes on sawfish ecology

Synopsis Pristis microdon, P. zijsron, P. clavata and Anoxypristis cuspidata are distributed throughout the Queensland section of the Gulf of Carpentaria, Australia. In a survey of the four species, Anoxypristis cuspidata was the most abundant and was recorded in both the inshore and offshore set net fisheries. The size distribution and catch locations of A. cuspidata suggest that the inshore area to a depth of 10 m may be the preferred habitat for juveniles of this species, while adults primarily occur offshore. Pristis microdon, P. zijsron and P. clavata were recorded only in the inshore fishery with catches dominated by immature animals. Pristis microdon was caught in the inshore fishery late in the monsoonal wet season (February to April) and inhabited both freshwater and estuarine environments. Pristis zijsron occurred only on the sand and mud flats outside river mouths whilst P. clavata inhabited both the sand and mud flats and upstream estuarine habitats. Observations on reproductive staging and the capture of neonate specimens suggest that in all four pristids, pupping occurred through the wet season until the beginning of the dry season in May. A seasonal set net closure for the barramundi, Lates calcarifer and shark fisheries, which has been in place since 1980 in Queensland Gulf waters, therefore offers a measure of protection to breeding female sawfish and their offspring.     

Parasites as indicators of movement and population connectivity of a non-diadromous, tropical estuarine teleost: king threadfin Polydactylus macrochir

Temporal and spatial patterns in parasite assemblages were examined to evaluate the degree of movement and connectivity of post-recruitment life-history stages of a large, non-diadromous tropical estuarine teleost, king threadfin Polydactylus macrochir, collected from 18 locations across northern Australia. Ten parasites types (juvenile stages of two nematodes and seven cestodes, and adults of an acanthocephalan) were deemed to be suitable for use as biological tags, in that they were considered to have a long residence time in the fish, were relatively easy to find and were morphologically very different to each other which aided discrimination. Univariate and discriminant function analysis of these parasites revealed little difference in temporal replicates collected from five locations, suggesting that the parasite communities were stable over the timeframes explored. Univariate, discriminant function, and Bray-Curtis similarity analyses indicated significant spatial heterogeneity, with Bray-Curtis classification accuracies ranging from 55 to 100% for locations in north-western and northern Australia, 24 to 88% in the Gulf of Carpentaria, and 39 to 88% on the east coast of Queensland. Few differences were observed among locations separated by <200 km. The observed patterns of parasite infection are in agreement with concurrent studies of movement and connectivity of P. macrochir in that they indicate a complex population structure across northern Australia. These results should be considered when reviewing the management arrangements for this species.     

Land management affects grass biomass in the Eucalyptus tetrodonta savannas of monsoonal Australia

Abstract We surveyed herbaceous biomass across the range of Eucalyptus tetrodonta savannas in north‐western Australia. Sample sites (n = 211) were stratified within four broad geographical regions characterized by different mixes of land management regimes. Grasses dominated (87% mean) the herbaceous biomass. After controlling for climatic and edaphic gradients, herbaceous biomass was highest in the Greater Darwin region (2.2 t ha⁻¹) which is managed predominantly by Europeans, and least under semi‐traditional Aboriginal management in Arnhem Land region (1.1 t ha⁻¹). In the drier Gulf of Carpentaria and Kimberley regions, where a mix of Aboriginal, conservation and pastoral land uses occurs, fuel loads were higher than in Arnhem Land region but still considerably lower than around Darwin. Sarga was recorded in all regions except the Gulf of Carpentaria and had the highest biomass in Darwin (0.88 t ha⁻¹) and lowest biomass in the Kimberley (0.54 t ha⁻¹). The proportion of herbaceous biomass made up of perennial grasses was least in Darwin (17%) and greatest in the Gulf (77%) regions. We suggest that climate, soils and land management account for differences between the drier pastoral regions of the Gulf of Carpentaria and the Kimberley and the wet Greater Darwin region relative to the Arnhem Land region. The high frequency, and larger spatial scale, of fires in the Greater Darwin region relative to the Arnhem Land region underpins the contrasting trends in total herbaceous biomass and abundance of flammable annual grasses.     

<Emphasis Type="Italic">Malalophus jensenae</Emphasis> n. g., n. sp. (Monogenea: Monocotylidae) from the gills of <Emphasis Type="Italic">Aetomylaeus vespertilio</Emphasis> (Myliobatidae) off northern Australia

Malalophus jensenae n. g., n. sp. is described from the gills of the ornate eagle ray Aetomylaeus vespertilio (Bleeker) collected off the eastern coast of the Gulf of Carpentaria, northern Queensland. The new genus is similar to Heliocotyle Neifar, Euzet & Ben Hassine, 1999, with which it shares a haptor bearing seven peripheral loculi and a single dorsal haptoral accessory structure. M. jensenae can be distinguished from species of Heliocotyle by the presence of numerous sclerotised sinuous ridges covering the ventral surfaces of the peripheral loculi of the haptor. It also lacks pseudosepta which are present on the haptor of Heliocotyle species. This is the first published record of a monogenean from an elasmobranch in the Gulf of Carpentaria, Australia.     

Stable isotopes differentiate bottlenose dolphins off west-central Florida

Distinguishing discrete population units among continuously distributed coastal small cetaceans is challenging and crucial to conservation. We evaluated the utility of stable isotopes in assessing group membership in bottlenose dolphins (Tursiops truncatus) off west-central Florida by analyzing carbon, nitrogen, and sulfur isotope values (δ¹³C, δ¹⁵N, and δ³⁴S) of tooth collagen from stranded dolphins. Individuals derived from three putative general population units: Sarasota Bay (SB), nearshore Gulf of Mexico (GULF), and offshore waters (OFF). Animals of known history (SB) served to ground truth the approach against animals of unknown history from the Gulf of Mexico (GULF, OFF). Dolphin groups differed significantly for each isotope. Average δ¹³C values from SB dolphins (−10.6‰) utilizing sea grass ecosystems differed from those of GULF (−11.9‰) and OFF (−11.9‰). Average δ¹⁵N values of GULF (12.7‰) and OFF (13.2‰) were higher than those of SB dolphins (11.9‰), consistent with differences in prey trophic levels. δ³⁴S values showed definitive differences among SB (7.1‰), GULF (11.3‰), and OFF (16.5‰) dolphins. This is the first application of isotopes to population assignment of bottlenose dolphins in the Gulf of Mexico and results suggest that isotopes may provide a powerful tool in the conservation of small cetaceans.     

Stock discrimination of Southern Garfish (Hyporhamphus melanochir) by stable isotope ratio analysis of otolith aragonite

Stable isotope analysis (δ¹⁸O and δ¹³C) of otolith aragonite was used to infer ontogenetic patterns of movement, delineate sub-population structure, and determine the mixing of Southern Garfish (Hyporhamphus melanochir) in South Australian waters. Adult garfish from the 2+ age class were collected from three sites within each of six regions along the South Australian coast: Northern Gulf St. Vincent, South West Gulf St. Vincent, Kangaroo Island, Northern Spencer Gulf, South West Spencer Gulf and the West Coast of Eyre Peninsula. Significant spatial variation was detected in mean δ¹⁸O and δ¹³C values among sites within regions and as a function of fish age. Salinity, rather than sea surface temperature, appeared to account for regional variation in δ¹⁸O, whereas variation in diet and metabolic processes were suggested to account for observed differences in δ¹³C. Otolith oxygen and carbon stable isotope values indicated that the South Australian Southern Garfish fishery is comprised of multiple, regional, population components that persist through time. Both the West Coast and Northern Spencer Gulf regions constitute distinct population components that exhibit little inter-regional mixing and therefore may be considered as discrete management units. The South West Spencer Gulf region may also be considered a separate population component, however, its level of connectivity with Gulf St. Vincent is uncertain. With the exception of juvenile garfish from Kangaroo Island, there was no clear regional separation within Gulf St. Vincent.     

δ15N of estuarine fishes as a quantitative indicator of urbanization

Nitrogen stable isotope values (δ¹⁵N) have commonly been used as a qualitative indicator of catchment urbanization in estuaries, but no quantitative relationship has to date been established between δ¹⁵N and degree of urbanization. We sampled five species of common estuarine fish (Mugil cephalus, Acanthopagrus australis, Sillago ciliata, Gerres subfasciatus and Herklotsichthys castelnaui) of different trophic levels from six estuaries in Southeast Queensland, Australia, to test if a quantitative relationship exists between fish δ¹⁵N and urbanization in the catchment. Degree of urbanization (urban %) in the catchment adjacent to the tidal estuary was measured using polygons constructed in Google Earth images, and verified using data from the detailed Queensland Land Use Mapping Project (QLUMP). Significant linear relationships exist between fish δ¹⁵N and urban % in most cases irrespective of the section of the estuary (upper, middle and lower) where the fish were caught, with no difference in slope and elevation between lines established for different sections. Inclusion of additional fish δ¹⁵N data from other Australian estuaries in a combined multiple regression model adding trophic level as a predictor generated a significant relationship predicting increase in fish δ¹⁵N values with increasing urban % and trophic level. There is therefore a generic quantitative relationship between estuarine fish δ¹⁵N values and degree of urbanization applicable to different fish species, geographic location or feeding habit. While the generality of this relationship needs to be tested further in other geographic locations, our findings potentially improve the applicability of fish δ¹⁵N values as a quantitative indicator of urban influence in estuaries.     

Temporal and spatial variation of plankton abundance in the Gulf of Carpentaria, Australia 1975-1977

The Gulf of Carpentaria is a large (ca. 3.7 x 10⁵ km²) shallow(<70 m) embayment in tropical northern Australia lying between11 and 17.5°S latitude. Although it contains a multi-speciespenaeid prawn fishery which is Australia's largest and mostvaluable fishery its hydrology and planktology are largely unknown.As a background to a study of the larval ecology of penaeidstocks, ten Gulf-wide survey cruises, sampling the planktonand hydrography, were undertaken over a twenty month periodfrom August 1975 to May 1977. Though comparisons with otherstudies are difficult because of variations in sampling techniquesand biomass estimation methods, the plankton biomass in theGulf of Carpentaria appears to be high by comparison with otherareas around Australia. The mean estimate over all stationsand all cruises of 77 mg/m³ dry weight (1880 mg/m²) compareswith the very high abundances found only in seasonal upwellingareas south of Java and off the northwest shelf of Australia.Further, the Gulf of Carpentaria standing stocks of planktoncompare with other coastal areas supporting important fisheriesoff the west coast of North America, the eastern North AtlanticOcean and some European waters. Because of its depth, relativelyhigh temperature and primary production rates, secondary productionrates are assumed to be high as well but as yet are unmeasured. ^*Microfiche of station list available upon request. CSIRO MarineLaboratories Reprint No. 1280     

A new species of Acanthobothrium van Beneden, 1850 (Tetraphyllidea: Onchobothriidae) from Pastinachus atrus (Macleay) (Batoidea: Dasyatidae) in Australian waters, with a reassessment of the host associations of Acanthobothrium spp. parasitising Pastinachus spp

A new Category 1 species of Acanthobothrium van Beneden, 1850 is described from the cowtail stingray Pastinachus atrus (Macleay) collected from the Gulf of Carpentaria near Weipa, Queensland, Australia. This species is unique among Acanthobothrium Category 1 species in that it retains gravid proglottids on its strobila. It differs further from the 34 other Category 1 species in total length, proglottid number and testis number. The host identities of other Acanthobothrium species reported from Pastinachus are revised based on recent taxonomic work on rays of this genus. Given the revised host taxonomy, according to which P. atrus is the only member of its genus occurring off Australia, this should be considered to be the fifth species of Acanthobothrium reported from this Australian endemic species.     

Insights into the functional role of fungi in deep-sea hydrothermal vents through the analysis of stable isotopes of carbon,nitrogen, and sulfur

The functional diversity of fungi remains poorly explored in the deep-sea, particularly in hydrothermal vents. Here, we approached this gap through the analysis of stable isotopes of carbon (δ¹³C), nitrogen (δ¹⁵N), and sulfur (δ³⁴S) of fourteen isolates obtained from three deep-sea vent systems of the southern Gulf of California. The δ¹³C results indicated that 60% of the isolates relied on mixed carbon sources fixed by the Calvin-Benson-Bassham and the reductive Tricarboxylic Acid (rTCA) cycles, whereas 40% relied exclusively on rTCA carbon. The δ¹⁵N and δ³⁴S values suggested a dependence on local and external nitrogen sources and the assimilation of chemosynthetic and photosynthetic inputs. Fungal δ¹³C and δ¹⁵N overlapped with those of primary and secondary vent macroconsumers, implying the assimilation of bacterial and invertebrate necromass and their ecological role as parasites. These findings provide insights into the unexplored trophic versatility of fungi in chemosynthetic ecosystems, highlighting their importance in deep-sea trophic dynamics.     

Oceanic interchange and nonequilibrium population structure in the estuarine dependent Indo-Pacific tasselfish,Polynemus sheridani

We assayed mtDNA haplotype [300 base pairs (bp) control region] geography and genealogy in the Indo-Pacific tasselfish, Polynemus sheridani from its contiguous estuarine distribution across northern Australia (n = 169). Eight estuaries were sampled from three oceanographic regions (Timor Sea, Gulf of Carpentaria and the Coral Sea) to assess the impact of Pleistocene sea level changes on the historical connectivity among P. sheridani populations. Specifically, we investigated the genetic consequences of disruption to Indian-Pacific Ocean connectivity brought about by the closure of the Torres Strait. Overall there was significant population subdivision among estuaries (FST = 0.161, PhiST = 0.187). Despite a linear distribution, P. sheridani did not show isolation by distance over the entire sampled range because of genetic similarity of estuaries greater than 3000 km apart. However, significant isolation by distance was detected between estuaries separated by less than 3000 km of coastline. Unlike many genetic studies of Indo-Pacific marine species, there was no evidence for an historical division between eastern and western populations. Instead, phylogeographical patterns were dominated by a starlike intraspecific phylogeny coupled with evidence for population expansion in both the Gulf of Carpentaria and the Coral Sea but not the Timor Sea. This was interpreted as evidence for recent west to east recolonization across of northern Australia following the last postglacial marine advance. We argue that although sufficient time has elapsed postcolonization for populations to approach gene flow-drift equilibrium over smaller spatial scales (< 3000 km), the signal of historical colonization persists to obscure the expected equilibrium pattern of isolation by distance over large spatial scales (> 3000 km).     

Spatio-temporal patterns of Barmah Forest virus disease in Queensland, Australia

Background

Barmah Forest virus (BFV) disease is a common and wide-spread mosquito-borne disease in Australia. This study investigated the spatio-temporal patterns of BFV disease in Queensland, Australia using geographical information system (GIS) tools and geostatistical analysis.

Methods/Principal Findings

We calculated the incidence rates and standardised incidence rates of BFV disease. Moran''s I statistic was used to assess the spatial autocorrelation of BFV incidences. Spatial dynamics of BFV disease was examined using semi-variogram analysis. Interpolation techniques were applied to visualise and display the spatial distribution of BFV disease in statistical local areas (SLAs) throughout Queensland. Mapping of BFV disease by SLAs reveals the presence of substantial spatio-temporal variation over time. Statistically significant differences in BFV incidence rates were identified among age groups (χ² = 7587, df = 7327,p<0.01). There was a significant positive spatial autocorrelation of BFV incidence for all four periods, with the Moran''s I statistic ranging from 0.1506 to 0.2901 (p<0.01). Semi-variogram analysis and smoothed maps created from interpolation techniques indicate that the pattern of spatial autocorrelation was not homogeneous across the state.

Conclusions/Significance

This is the first study to examine spatial and temporal variation in the incidence rates of BFV disease across Queensland using GIS and geostatistics. The BFV transmission varied with age and gender, which may be due to exposure rates or behavioural risk factors. There are differences in the spatio-temporal patterns of BFV disease which may be related to local socio-ecological and environmental factors. These research findings may have implications in the BFV disease control and prevention programs in Queensland.     

French naiad (Bivalvia: Margaritiferidae,Unionidae) species distribution models: prediction maps as tools for conservation

The aim of this study was to determine whether juvenile scalloped hammerhead sharks (Sphyrna lewini) use the south-eastern Gulf of California as a nursery and feeding area. This information could help lay the groundwork required for the conservation of this endangered species. To address this, we carried out stable isotope (δ¹⁵N and δ¹³C) and stomach content analyses of sharks caught between 2000 and 2004 in Mazatlan, Mexico. Stomach contents and δ¹³C values indicated that S. lewini is a predator that feeds on benthic prey near the coast. Differences in δ¹⁵N average values between sizes classes (<100 vs. >100 cm) suggest that there was an ontogenetic change in this shark’s feeding habits and also in their living environment (from benthic areas to pelagic areas). The trophic position indicated that S. lewini is a tertiary consumer, but with a high degree of trophic plasticity, and thus, different trophic roles, highlighting the importance of this predator as a regulator of prey populations. Finally, the linear isotopic relationship between S. lewini and its prey indicates a long residency within the Mazatlan area. Our results demonstrate that the south-eastern Gulf of California is a nursery area that offers abundant food for juvenile scalloped hammerhead sharks.     

Tracing energy flow in stream food webs using stable isotopes of hydrogen

1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (δD) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in δD of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in δD in stream food webs in a forested catchment where variation in δ¹³C has been described previously. 3. Although algal δD varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67‰) from terrestrial carbon sources. Environmental conditions known to affect algal δ¹³C, such as water velocity and stream productivity did not greatly influence algal δD, and there was no evidence of seasonal variation. In contrast, algal δ¹³C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial δ¹³C in all streams with catchment areas larger than 10 km². 4. While knowledge of isotopic exchange with water and trophic fractionation of δD for aquatic consumers is limited, consistent source separation in streams suggests that δD may provide a complementary food web tracer to δ¹³C in aquatic food webs. Lack of significant seasonal or spatial variation in δD is a distinct advantage over δ¹³C for applications in many aquatic ecosystems.     

Molecular genetics to inform spatial management in benthic invertebrate fisheries: a case study using the Australian Greenlip Abalone

Hierarchical sampling and subsequent microsatellite genotyping of >2300 Haliotis laevigata (greenlip abalone) from 19 locations distributed across five biogeographic regions have substantially advanced our knowledge of population structure and connectivity in this commercially important species. The study has found key differences in stock structure of H. laevigata compared with the sympatric and congeneric Haliotis rubra (blacklip abalone) and yielded valuable insights into the management of fisheries targeting species characterized by spatial structure at small scales (i.e. S‐fisheries). As with H. rubra, H. laevigata comprise a series of metapopulations with strong self‐recruitment. However, the spatial extent of H. laevigata metapopulations (reefal areas around 30 km²; distances of up to 135 km are effective barriers to larval dispersal) was substantially greater than that identified for H. rubra (Miller et al. 2009). Differences in the dynamics and scale of population processes, even between congeneric haliotids as made evident in this study, imply that for S‐fisheries, it is difficult to generalize about the potential consequences of life history commonalities. Consequently, species‐specific management reflective of the population structure of the target species remains particularly important. This will likely require integration of information about stock structure and connectivity with data on life history and population dynamics to determine the necessary input (e.g. number of fishers, fishing effort) and output (e.g. minimum legal size, total allowable catch) controls to underpin their sustainable management.     

Red snapper management in the Gulf of Mexico: science- or faith-based?

The most controversial fishery in U.S. waters of the Gulf of Mexico (Gulf) is for northern red snapper Lutjanus campechanus, which collapsed in the late 1980s when stock biomass became too low to be fished commercially in the eastern Gulf. Red snapper management began in 1989; the stock is now showing signs of recovery. The Gulf of Mexico Fishery Management Council has been slow to sufficiently reduce catches of the directed fisheries to rebuild the stock in a timely fashion, although compliance with the Magnuson-Stevens Reauthorization Act of 2006 (MSRA) required substantial cuts in the harvest of red snapper beginning in 2007. In our opinion, this could have been avoided if conservative management practices had been adopted earlier. We believe that ‘faith-based fisheries’ arguments have been used to defer effective management of red snapper in the Gulf, which in turn has strained the relationship between science, management, and stakeholders there. We provide a simple empirical argument and alternate interpretations of a recently published perspective on the historical fishery of red snapper in the Gulf to conclude that the preponderance of evidence used in the agency stock assessment process, and the simple arguments made here, do not support the perspective that the red snapper stock has increased in size sufficiently to defer compliance with the MSRA.     

Spatial and temporal variability in ringed seal (Pusa hispida) stable isotopes in the Beaufort Sea

Arctic ecosystem dynamics are shifting in response to warming temperatures and sea ice loss. Such ecosystems may be monitored by examining the diet of upper trophic level species, which varies with prey availability. To assess interannual variation in the Beaufort Sea ecosystem, we examined spatial and temporal trends in ringed seal (Pusa hispida) δ¹³C and δ¹⁵N in claw growth layers grown from 1964 to 2011. Stable isotopes were correlated with climate indices, environmental conditions, seal population productivity, and geographic location. Sex and age did not influence stable isotopes. Enriched ¹³C was linked to cyclonic circulation regimes, seal productivity, and westward sampling locations. Higher δ¹⁵N was linked to lower sea surface temperatures, a higher percentage of pups in the subsistence harvest, and sample locations that were eastward and further from shore. From the 1960s to 2000s, ringed seal niche width expanded, suggesting a diversification of diet due to expansion of prey and/or seal space use. Overall, trends in ringed seal stable isotopes indicate changes within the Beaufort Sea ecosystem affected by water temperatures and circulation regimes. We suggest that continued monitoring of upper trophic level species will yield insights into changing ecosystem structure with climate change.