Species-specific effects of four preservative treatments on oocytes and ovarian material of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and American plaice (Hippoglossoides platessoides)

The lack of information concerning the preservation of ovarian material of fish species inhibits standardization of methods for determining fecundity and measuring oocytes. The effects of four preservatives (10% phosphate-buffered formalin, modified Gilson’s solution, 70% ethanol, and freezing) on ovarian material weight and oocyte size were quantified for prespawning Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and American plaice (Hippoglossoides platessoides). Effects of preservation were similar between Atlantic cod and haddock but different between Atlantic cod and American plaice for nearly all comparisons. Although all treatments affected the weight of ovarian material, freezing caused the most change and formalin caused the least. Such signif icant species-specific effects should be quantified in the calculation of life history characteristics, such as fecundity, to minimize error. This is one of few studies dedicated to evaluating the effects of preservation on oocytes and ovarian material and is the first to evaluate multiple preservatives on species

Fine-scale taxonomic and spatiotemporal variability in the energy density of prey for juvenile Chinook salmon (Oncorhynchus tshawytscha)

The growth and survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) are determined in part by biotic and abiotic conditions experienced during their first marine summer. Of the biotic conditions, the quality of available prey is integral for optimal growth and survival. Current studies that investigate the effect of variable prey quality on salmon growth approximate energy density using literature values. This approach ignores fine-scale taxonomic as well as spatial and temporal differences in prey quality. To address these possible sources of error, monthly zooplankton tows were performed in Saanich Inlet, Cowichan Bay and Maple Bay off the coast of Vancouver Island, British Columbia in the summer of 2017. Individuals were separated to the species level and wet, dry and ash weights were measured for each zooplankter. Energy density was calculated from an established model, which relates the ash-free dry weight of individuals to energy density values. Early results suggest statistically significant differences in energy density between several species of hyperiid amphipods, which represent a large proportion of O. tshawytscha diet in some years. Other important species groups such as euphausiids, crab zoea and gammerid amphipods differed in energy density from previously reported studies in other locations suggesting spatial variability in energy density. These early results suggest that fine-scale taxonomic variability in energy density exists and that species-specific energy density may vary across space and time. Studies that draw conclusions from literature values of energy density without direct measurement should be cautious in extrapolating with these data in relation to their study system

Rate of biological invasions is lower in coastal marine protected areas

Marine biological invasions threaten biodiversity worldwide. Here we explore how Marine Protected areas, by reducing human use of the coast, confer resilience against the introduction of non-indigenous species (NIS), using two very different Pacific islands as case studies for developing and testing mathematical models. We quantified NIS vectors and promoters on Vancouver (Canada) and Moorea (French Polynesia) islands, sampled and barcoded NIS, and tested models at different spatial scales with different types of interaction among vectors and between marine protection and NIS frequency. In our results NIS were negatively correlated with the dimension of the protected areas and the intensity of the protection. Small to medium geographical scale protection seemed to be efficient against NIS introductions. The likely benefit of MPAs was by exclusion of aquaculture, principally in Canada. These results emphasize the importance of marine protected areas for biodiversity conservation, and suggest that small or medium protected zones would confer efficient protection against NIS introduction

Recalculated diet and daily ration of the shortfin mako (Isurus oxyrinchus), with a focus on quantifying predation on bluefish (Pomatomus saltatrix) in the northwest Atlantic Ocean

The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance and availability are reflected in these two biological variables. During the summers of 2001 and 2002, stomach content data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared to index calculations from historical diet data collected from 1972 through 1983. Bluefish (Pomatomus saltatrix) were the predominant prey in the 1972–83 and 2001–02 diets, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001– 02 diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic demands. The daily energetic requirement was broken down by using a calculated energy content for the current diet of 4909 KJ/kg. Based on the proportional energy of bluefish in the diet by weight, an average shortfin mako consumes roughly 500 kg of bluefish per year off the northeast coast of the United States. The results are discussed in relation to the potential effect of intense shortfin mako predation on bluefish abundance in the region

Recalculated diet and daily ration of the shortfin mako (\u3cem\u3eIsurus oxyrinchus\u3c/em\u3e), with a focus on quantifying predation on bluefish (\u3cem\u3ePomatomus saltatrix\u3c/em\u3e) in the northwest Atlantic Ocean

The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance and availability are ref lected in these two biological variables. During the summers of 2001 and 2002, stomach content data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared to index calculations from historical diet data collected from 1972 through 1983. Bluefish (Pomatomus saltatrix) were the predominant prey in the 1972–83 and 2001–02 diets, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001– 02 diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic demands. The daily energetic requirement was broken down by using a calculated energy content for the current diet of 4909 KJ/kg. Based on the proportional energy of bluefish in the diet by weight, an average shortfin mako consumes roughly 500 kg of bluefish per year off the northeast coast of the United States. The results are discussed in relation to the potential effect of intense shortfin mako predation on bluefish abundance in the region

Reconstruction of original body size and estimation of allometric relationships for the longfin inshore squid (Loligo pealeii) and northern shortfin squid (Illex illecebrosus)

Quantification of predator-prey body size relationships is essential to understanding trophic dynamics in marine ecosystems. Prey lengths recovered from predator stomachs help determine the sizes of prey most influential in supporting predator growth and to ascertain size-specific effects of natural mortality on prey populations (Bax, 1998; Claessen et al., 2002). Estimating prey size from stomach content analyses is often hindered because of the degradation of tissue and bone by digestion. Furthermore, reconstruction of original prey size from digested remains requires species-specific reference materials and techniques. A number of diagnostic guides for freshwater (Hansel et al., 1988) and marine (Watt et al., 1997; Granadeiro and Silva, 2000) prey species exist; however they are limited to specific geographic regions (Smale et al., 1995; Gosztonyi et al., 2007). Predictive equations for reconstructing original prey size from diagnostic bones in marine fishes have been developed in several studies of piscivorous fishes of the Northwest Atlantic Ocean (Scharf et al., 1998; Wood, 2005). Conversely, morphometric relationships for cephalopods in this region are scarce despite their importance to a wide range of predators, such as finfish (Bowman et al., 2000 ; Staudinger, 2006), elasmobranchs (Kohler, 1987), and marine mammals (Gannon et al., 1997; Williams, 1999)

Seagrass nursery function enhanced by habitat connectivity

Seascape connectivity is an emerging feature influencing marine ecosystem function. Connectivity, via the interplay of habitat configuration, its physical structure, and associated food webs, may alter the provision of nursery habitat, influencing the success of fish populations and harvests thereof. We quantified the effects of adjacent habitat type on seagrass nurseries for rockfish. We compared seagrass sites with contrasting structure and productivity in adjacent habitats: kelp forest and sand. To elucidate the spatially-dependent flow of material in the seagrass meadow, we estimated the proportion of basal contributions (producers) to the food web using an isotopic mixing model on YOY (young-of-the-year) rockfish consumers. To estimate population responses to spatial connectivity, we enumerated YOY rockfish recruitment by SCUBA, alongside invertebrate prey and fish predators at all sites. Using GLMMS, we modelled the relative effects of adjacent habitat type, seagrass trophic interactions (prey availability and predator presence), and structural complexity, on YOY rockfish recruitment. We found that kelp carbon was the highest basal contributor to YOY rockfish consumers across all seagrass sites, but auxiliary contributions varied among site. YOY rockfish at highly complex and productive seagrass sites (adjacent to kelp forests and interior meadow) consumed higher quality prey, corresponding to increased body condition. Adjacency to kelp forests, seagrass structural complexity, and prey biomass increased YOY rockfish densities. However, the positive effect of kelp adjacency was dampened by seagrass complexity; likely due to predator spill-over into complex seagrass habitat. Overall, recruitment and trophic dynamics (e.g. basal contributions, prey-predators interactions) in the seagrass meadow were influenced by seascape configuration, revealing that nursery function is spatially-mediated by adjacent habitats, and their structural complexity and productivity. With declining marine habitats worldwide, we illustrate the importance of considering connectivity among nearshore habitats for conservation planning, supporting an ecosystem approach that considers the full seascape matrix of intermixed habitats

Passive reclamation of soft-sediment ecosystems on the North Coast of British Columbia, Canada

Estuarine ecosystems are degraded through anthropogenic development, leading to reduced habitat suitability for biological communities. The Skeena River estuary (British Columbia, Canada) is undergoing passive reclamation from historical salmon canneries and pulp mills, while localized disturbances continue at present. To reveal both current impacts and the trajectory of passive reclamation from historical activities, the intertidal mudflat surrounding the longest operating salmon cannery, Cassiar Cannery, within the Skeena estuary was surveyed. Nutrient availability (chlorophyll a concentration/organic matter content), sediment variables (particle size, water content, penetrability, woody debris/macroalgae cover, apparent redox potential discontinuity depth), and infaunal community composition varied spatiotemporally, and suggest that an old dock may be influencing the infaunal community given the abundance of disturbance indicating taxa below the dock. However, with populations of amphipods, mobile polychaetes, and a complex community structure, the mudflat as a whole appears to be relatively healthy. Therefore, cessation of historic activities has allowed for passive reclamation to a reasonably unstressed state, though a threshold of recovery may exist for intertidal mudflats beyond which passive reclamation will not be effective

Human Consumption of Microplastics

Microplastics are ubiquitous across ecosystems, yet the exposure risk to humans is unresolved. Focusing on the American diet, we evaluated the number of microplastic particles in commonly consumed foods in relation to their recommended daily intake. The potential for microplastic inhalation and how the source of drinking water may affect microplastic consumption were also explored. Our analysis used 402 data points from 26 studies, which represents over 3600 processed samples. Evaluating approximately 15% of Americans’ caloric intake, we estimate that annual microplastics consumption ranges from 39000 to 52000 particles depending on age and sex. These estimates increase to 74000 and 121000 when inhalation is considered. Additionally, individuals who meet their recommended water intake through only bottled sources may be ingesting an additional 90000 microplastics annually, compared to 4000 microplastics for those who consume only tap water. These estimates are subject to large amounts of variation; however, given methodological and data limitations, these values are likely underestimates

Staging ovaries of Haddock (Melanogrammus aeglefinus): implications for maturity indices and field sampling practices

We build on recent efforts to standardize maturation staging methods through the development of a field-proof macroscopic ovarian maturity index for Haddock (Melanogrammus aeglefinus) for studies on diel spawning periodicity. A comparison of field and histological observations helped us to improve the field index and methods, and provided useful insight into the reproductive biology of Haddock and other boreal determinate fecundity species. We found reasonable agreement between field and histological methods, except for the regressing and regenerating stages (however, differentiation of these 2 stages is the least important distinction for determination of maturity or reproductive dynamics). The staging of developing ovaries was problematic for both methods partly because of asynchronous oocyte hydration during the early stage of oocyte maturation. Although staging on the basis of histology in a laboratory is generally more accurate than macroscopic staging methods in the field, we found that field observations can uncover errors in laboratory staging that result from bias in sampling unrepresentative portions of ovaries. For 2 specimens, immature ovaries observed during histological examination were incorrectly assigned as regenerating during macroscopic staging. This type of error can lead to miscalculation of length at maturity and of spawning stock biomass, metrics that are used to characterize the state of a fish population. The revised field index includes 3 new macroscopic stages that represent final oocyte maturation in a batch of oocytes and were found to be reliable for staging spawning readiness in the field. The index was found to be suitable for studies of diel spawning periodicity and conforms to recent standardization guidelines