Groups Of Marine Mammals Research Articles

Observations of Weddell seal (Leptonychotes weddellii) supernumerary nipples

A wide variety of nipple locations and configurations exist among pinnipeds. Like all marine mammals, pinnipeds can have supernumerary nipples that form in utero. Supernumerary nipples have been documented in several species of pinnipeds, the only taxonomic group of marine mammals with variation in nipple number. We document multiple observations (n = 4) of female Weddell seals (Leptonychotes weddellii) with supernumerary nipples in Erebus Bay, Antarctica, including a female Weddell seal with four nipples that was observed nursing two pups. Intraspecific variation in the number of supernumerary nipples observed included both one and two supernumerary nipples. The majority of the observed supernumerary nipples were nursed on by pups, but lactation was unable to be confirmed. These are the first documented observations of supernumerary nipples in Weddell seals.

Exploring biodiversity patterns in a marine and coastal protected area: Implications for management within and outside MCPAs

Identifying patterns and understanding the processes associated with Marine and Coastal Protected Areas (MCPAs) (local scale) are essential for developing specific hypotheses about trophic interactions and potential cascading effects of local and global changes. This can also serve as an initial step in the identification of biodiversity patterns and biological interactions on a regional scale. This study characterized a set of species/taxa composed of four subcommunities featuring macrobenthic infauna, epibenthic megafauna, birds, and mammals observed between 2019 and 2021 in the estuarine and marine system of the Pitipalena-Añihué MCPA in Chilean Patagonia. Biodiversity patterns were analyzed using multidimensional models and indices.A pool of 276 taxa were observed within the studied subcommunities, and reproduction was confirmed for several bird and mammal species (mostly on islets). The results indicate a system with several types of habitats, where the sea lion Otaria flavescens was dominant among the group of marine mammals. Notably, birds and epibenthic megafauna showed differences between the marine and estuarine environment. The observed biodiversity patterns can be attributed to environmental heterogeneity, as well as anthropic effects (including invasive species, fishing, and aquaculture). This work proposes a synthesized spatial distribution scheme of the main taxa, complemented by a matrix of hypothetical trophic interactions. Along with demonstrating the current lack of available information, this matrix offers an opportunity to assess the ecosystem's sensitivity, identify relevant information gaps, and develop hypotheses about specific trophic interactions (scalable to the region) and the potential cascading effects of ocean changes.

Underwater noise characteristics of offshore exploratory drilling and its impact on marine mammals

Geotechnical survey is an important prerequisite to the construction of offshore wind farms. However, the impact of underwater survey noises has not yet been studied in details. In this paper, we studied transmission of underwater noises from offshore exploratory drilling (OED) at the Xiamen port. The noises were categorized into three types: hammering noises (hammering down of casings, which were 180-mm diameter steel pipes), vibrating noises (vibration of casings that had been hammered down), and drilling noises (generated during the borehole drilling process). We considered the variation in intensity of these three noise types, and set up two fixed and one movable stations to measure and analyze the source and propagation characteristics of these noises. The results indicate that hammering noise is an impulsive sound with a dominant frequency below 10 kHz, and source levels (SLs) of 197.1 dB re 1μPa @ 1 m (rms over 95% energy duration. 1–64,000 Hz) and 212.9 dB re 1μPa @ 1 m (peak). Vibrating and drilling noises are non-impulsive sounds with the fundamental frequencies of 41 Hz and 45 Hz, and SLs of 158.9 dB re 1μPa rms @ 1 m and 155.9 dB re 1μPa rms @ 1 m, respectively. The impact assessment of OED noises on five groups of marine mammals with different audible frequency ranges (Low (LF), High (HF), and Very High (VHF) frequency cetaceans, sirenians (SI), and phocid pinnipeds (PW)) demonstrates that hammering noise can induce a high risk of hearing damage to their hearing, at as far as 300 meters for VHF group, while drilling noise can only induce hearing damage at about 40 meters. Marine mammals are susceptible to behavior alteration, with a detectable distance of 1.9 km from the source, and it is recommended to set a warning zone with a radius of 1.9 km during OED construction.

What are the Metabolic Rates of Marine Mammals and What Factors Impact this Value: A review.

Over the past several decades, scientists have constructed bioenergetic models for marine mammals to assess potential population-level consequences following exposure to a disturbance, stressor, or environmental change, such as under the Population Consequences of Disturbance (pCOD) framework. The animal's metabolic rate (rate of energy expenditure) is a cornerstone for these models, yet the cryptic lifestyles of marine mammals, particularly cetaceans, have limited our ability to quantify basal (BMR) and field (FMR) metabolic rates using accepted 'gold standard' approaches (indirect calorimeter via oxygen consumption and doubly labeled water, respectively). Thus, alternate methods have been used to quantify marine mammal metabolic rates, such as extrapolating from known allometric relationships (e.g. Kleiber's mouse to elephant curve) and developing predictive relationships between energy expenditure and physiological or behavioral variables. To understand our current knowledge of marine mammal metabolic rates, we conducted a literature review (1900-2023) to quantify the magnitude and variation of metabolic rates across marine mammal groups. A compilation of data from studies using 'gold standard' methods revealed that BMR and FMR of different marine mammal species ranges from 0.2 to 3.6 and 1.1 to 6.1 x Kleiber, respectively. Mean BMR and FMR varied across taxa; for both measures odontocete levels were intermediate to higher values for otariids and lower values of phocids. Moreover, multiple intrinsic (e.g. age, sex, reproduction, molt, individual) and extrinsic (e.g. food availability, water temperature, season) factors, as well as individual behaviors (e.g. animal at water's surface or submerged, activity level, dive effort and at-sea behaviors) impact the magnitude of these rates. This review provides scientists and managers with a range of reliable metabolic rates for several marine mammal groups as well as an understanding of the factors that influence metabolism to improve the discernment for inputs into future bioenergetic models.

Assessing potential perception of shipping noise by marine mammals in an arctic inlet.

Shipping is increasing in Arctic regions, exposing marine mammals to increased underwater noise. Noise analyses often use unweighted broadband sound pressure levels (SPL) to assess noise impacts, but this does not account for the animals' hearing abilities at different frequencies. In 2018 and 2019, noise levels were recorded at five and three sites, respectively, along a shipping route in an inlet of Northern Baffin Island, Canada. Broadband SPLs (10 Hz-25 kHz), unweighted and with auditory weighing functions from three marine mammal groups, were compared between times ore carriers (travelling < 9 knots) were present or absent. Clearly audible distances of shipping noise and exposure durations were estimated for each weighting function relative to vessel direction, orientation, and year. Auditory weighting functions had significant effects on the potential perception of shipping noise. Bowhead whales (Balaena mysticetus) experienced similar SPLs to unweighted levels. Narwhals (Monodon monoceros) and ringed seals (Pusa hispida) experienced lower SPLs. Narwhals were unlikely to clearly perceive shipping noise unless ships were in close proximity (<3 km) and ambient noise levels were low. Detectability propagation models of presumed noise exposure from shipping must be based on the hearing sensitivities of each species group when assessing noise impacts on marine mammals.

Marine mammal sensory systems: Special issue overview.

Marine mammals are a unique group of organisms that are secondarily adapted to the aquatic environment. Their specific lifestyle requires numerous adaptations of anatomy and physiology in general, and sensory physiology in particular. During the course of evolution, marine mammal senses changed to fit with the specific requirements of underwater sensing, while at the same time retaining aerial sensing to various degrees. In this special issue, state of the art science in the field of marine mammal sensory research is reported for representatives of all marine mammal groups, unfortunately with the exclusion of the polar bear. The articles focus on somatosensation of the glabrous skin of cetaceans and mechanoreception, including haptics, hydrodynamics, and acoustics, to chemoreception. Articles even deal with electroreception, highlighting that the bottlenose dolphin can perceive weak electric stimuli, and vision, indicating that harbor seals are able to derive temporal information from an optical stimulus. Altogether this special issue illustrates the diversity of research in the field regarding sensory systems, species, or experimental approaches. The strength of this special issue lies in the combination of carefully conducted anatomical studies paired with observations and behavioral studies attempting to relate "form" and "function" as well as in the many impulses and future avenues mentioned by numerous contributions.

Selection of a reference gene for studies on lipid-related aquatic adaptations of toothed whales (Grampus griseus).

Toothed whales are one group of marine mammals that has developed special adaptations, such as echolocation for predation, to successfully live in a dynamic aquatic environment. Their fat metabolism may differ from that of other mammals because toothed whales have acoustic fats. Gene expression in the metabolic pathways of animals can change with respect to their evolution and environment. A real‐time quantitative polymerase chain reaction (RT‐qPCR) is a reliable technique for studying the relative expressions of genes. However, since the accuracy of RT‐qPCR data is totally dependent on the reference gene, the selection of the reference gene is an essential step. In this study, 10 candidate reference genes (ZC3H10, FTL, LGALS1, RPL27, GAPDH, FTH1, DCN, TCTP, NDUS5, and UBIM) were initially tested for amplification efficiency using RT‐qPCR. After excluding DCN, the remaining nine genes, which are nearly 100% efficient, were selected for the gene stability analysis. Stable reference genes across eight different fat tissue, liver, and muscle samples from Grampus griseus were identified by four algorithms, which were provided in Genorm, NormFinder, BestKeeper, and Delta CT. Finally, a RefFinder comprehensive ranking was performed based on the stability values, and the nine genes were ranked as follows: LGALS1 > FTL > GAPDH > ZC3H10 > FTH1 > NDUS5 > TCTP > RPL27 > UBIM. The LGALS1 and FTL genes were identified as the most stable novel reference genes. The third‐ranked gene, GAPDH, is a well‐known housekeeping gene for mammals. Ultimately, we suggest the use of LGALS1 as a reliable novel reference gene for genomics studies on the lipid‐related aquatic adaptations of toothed whales.

Comparative Study of the Gut Microbiota Among Four Different Marine Mammals in an Aquarium.

Despite an increasing appreciation in the importance of host–microbe interactions in ecological and evolutionary processes, information on the gut microbial communities of some marine mammals is still lacking. Moreover, whether diet, environment, or host phylogeny has the greatest impact on microbial community structure is still unknown. To fill part of this knowledge gap, we exploited a natural experiment provided by an aquarium with belugas (Delphinapterus leucas) affiliated with family Monodontidae, Pacific white-sided dolphins (Lagenorhynchus obliquidens) and common bottlenose dolphin (Tursiops truncatus) affiliated with family Delphinidae, and Cape fur seals (Arctocephalus pusillus pusillus) affiliated with family Otariidae. Results show significant differences in microbial community composition of whales, dolphins, and fur seals and indicate that host phylogeny (family level) plays the most important role in shaping the microbial communities, rather than food and environment. In general, the gut microbial communities of dolphins had significantly lower diversity compared to that of whales and fur seals. Overall, the gut microbial communities were mainly composed of Firmicutes and Gammaproteobacteria, together with some from Bacteroidetes, Fusobacteria, and Epsilonbacteraeota. However, specific bacterial lineages were differentially distributed among the marine mammal groups. For instance, Lachnospiraceae, Ruminococcaceae, and Peptostreptococcaceae were the dominant bacterial lineages in the gut of belugas, while for Cape fur seals, Moraxellaceae and Bacteroidaceae were the main bacterial lineages. Moreover, gut microbial communities in both Pacific white-sided dolphins and common bottlenose dolphins were dominated by a number of pathogenic bacteria, including Clostridium perfringens, Vibrio fluvialis, and Morganella morganii, reflecting the poor health condition of these animals. Although there is a growing recognition of the role microorganisms play in the gut of marine mammals, current knowledge about these microbial communities is still severely lacking. Large-scale research studies should be undertaken to reveal the roles played by the gut microbiota of different marine mammal species.

Behavioral and anatomical evidence for electroreception in the bottlenose dolphin (Tursiops truncatus).

In the order of cetacean, the ability to detect bioelectric fields has, up to now, only been demonstrated in the Guiana dolphin (Sotalia guianensis) and is suggested to facilitate benthic feeding. As this foraging strategy has also beenreported for bottlenose dolphins (Tursiops truncatus), we studied electroreceptionin this species by combining an anatomical analysis of "vibrissal crypts" as potential electroreceptors from neonate and adult animals with a behavioral experiment. In the latter, four bottlenose dolphins were trained on a go/no-go paradigm with acoustic stimuli and afterward tested for stimulus generalization within and across modalities using acoustic, optical, mechanical, and electric stimuli. While neonates still possess almost complete vibrissal follicles including a hair shaft, hair papilla, and cavernous sinus, adult bottlenose dolphins lack these features. Thus, their "vibrissal crypts" show a similar postnatal morphological transformation from a mechanoreceptor to an electroreceptor as in Sotalia. However, innervation density was high and almost equal in both, neonate as well as adult animals. In the stimulus generalization tests the dolphins transferred the go/no-go response within and across modalities. Although all dolphins responded spontaneously to the first presentation of a weak electric field, only three of them showed perfect transfer in this modality by responding continuously to electric field amplitudes of 1.5mV cm-1 , successively reduced to 0.5mV cm-1 . Electroreception can explain short-range prey detection in crater-feeding bottlenose dolphins. The fact that this is the second odontocete species with experimental evidence for electroreception suggests that it might be widespread in this marine mammal group.

Kin relationships in cultural species of the marine realm: case study of a matrilineal social group of sperm whales off Mauritius island, Indian Ocean.

Understanding the organization and dynamics of social groups of marine mammals through the study of kin relationships is particularly challenging. Here, we studied a stable social group of sperm whales off Mauritius, using underwater observations, individual-specific identification, non-invasive sampling and genetic analyses based on mitochondrial sequencing and microsatellite profiling. Twenty-four sperm whales were sampled between 2017 and 2019. All individuals except one adult female shared the same mitochondrial DNA (mtDNA) haplotype—one that is rare in the western Indian Ocean—thus confirming with near certainty the matrilineality of the group. All probable first- and second-degree kin relationships were depicted in the sperm whale social group: 13 first-degree and 27 second-degree relationships were identified. Notably, we highlight the likely case of an unrelated female having been integrated into a social unit, in that she presented a distinct mtDNA haplotype and no close relationships with any members of the group. Investigating the possible matrilineality of sperm whale cultural units (i.e. vocal clans) is the next step in our research programme to elucidate and better apprehend the complex organization of sperm whale social groups.

Why should we reconsider using species richness in spatial conservation prioritization?

Species richness has been largely used for determining site conservation values, but this has not been assessed in the context of marine mammal conservation. In our study, we assessed the effectiveness of species richness as a surrogate of marine mammal species representation at the global scale and compared it to the use of complementarity as an alternative approach. We obtained 134 marine mammal distribution maps from the IUCN Red List database and used two complementarity algorithms to calculate conservation priorities. To determine the effectiveness of species richness as a surrogate, we calculated the Species Accumulation Index (SAI) scores for marine mammal groups. Our findings indicate that both complementarity approaches are consistently more effective surrogates of marine mammal species representation across all groups and grains tested. Our study strongly supports the use of complementarity as supposed to richness as the preferred method to select sites conservation values for marine mammals. To the best of our knowledge, we are the first to assess the effectiveness of richness and compare it to results obtained by the use of complementarity in global marine mammal species spatial representation.

Contraction of the ROS Scavenging Enzyme Glutathione S-Transferase Gene Family in Cetaceans.

Cetaceans are a group of marine mammals whose ancestors were adaptated for life on land. Life in an aquatic environment poses many challenges for air-breathing mammals. Diving marine mammals have adapted to rapid reoxygenation and reactive oxygen species (ROS)-mediated reperfusion injury. Here, we considered the evolution of the glutathione transferase (GST) gene family which has important roles in the detoxification of endogenously-derived ROS and environmental pollutants. We characterized the cytosolic GST gene family in 21 mammalian species; cetaceans, sirenians, pinnipeds, and their terrestrial relatives. All seven GST classes were identified, showing that GSTs are ubiquitous in mammals. Some GST genes are the product of lineage-specific duplications and losses, in line with a birth-and-death evolutionary model. We detected sites with signatures of positive selection that possibly influence GST structure and function, suggesting that adaptive evolution of GST genes is important for defending mammals from various types of noxious environmental compounds. We also found evidence for loss of alpha and mu GST subclass genes in cetacean lineages. Notably, cetaceans have retained a homolog of at least one of the genes GSTA1, GSTA4, and GSTM1; GSTs that are present in both the cytosol and mitochondria. The observed variation in number and selection pressure on GST genes suggest that the gene family structure is dynamic within cetaceans.

Oldest record of monk seals from the North Pacific and biogeographic implications.

True seals (crown Phocidae) originated during the late Oligocene-early Miocene (approx. 27-20 Ma) in the North Atlantic/Mediterranean region, with later (middle Miocene, approx. 16-11 Ma) dispersal events to the South Atlantic and South Pacific. Contrasting with other pinnipeds, the fossil record of phocids from the North Pacific region is scarce and restricted to the Pleistocene. Here we present the oldest fossil record of crown phocids, monachines (monk seals), from the North Pacific region. The specimens were collected from the upper Monterey Formation in Southern California and are dated to 8.5-7.1 Ma, predating the previously oldest known record by at least 7 Ma. This record provides new insights into the early biogeographic history of phocids in the North Pacific and is consistent with a northward dispersal of monk seals (monachines), which has been recognized for other groups of marine mammals. Alternatively, this finding may correspond with a westward dispersal through the Central American Seaway of some ancestor of the Hawaiian monk seal. This record increases the taxonomic richness of the Monterey pinniped assemblage to five taxa, making it a fairly diverse fossil assemblage, but also constitutes the oldest record of sympatry among all three extant pinniped crown clades.

Practical implementation of auditory time and frequency weighting in marine bioacoustics

Much effort is currently directed at describing the behavioral reactions of marine mammals following exposure to sound with the aim of deriving generalized thresholds and dose-response functions. The perceived loudness of a given sound is a candidate for a common metric for sound exposure. The loudness of a signal relates to various factors, including the stimulus duration and frequency content, and it can be approximated by an appropriate time and frequency weighting of the signal. Auditory frequency weighting is achieved by applying a frequency weighting function (band-pass filter), with a frequency response resembling the shape of an inverted audiogram. Temporal weighting may be achieved by computing the running rms-average (Leq) with a time constant that is comparable to that of the mammalian auditory system. The practical implementation of such weighting functions are presented in the form of Matlab functions. These functions generate output signals that are weighted according to current recommendations for different groups of marine mammals. With these functions, it is possible to derive the weighted peak Leq of a signal, which is likely to be a good proxy for the loudness of the signal. Ultimately, this weighted level is conjectured to be a predictor of behavioral response of marine mammals to the sound.

Species-level classification and clustering of beaked whale echolocation recordings

The Littoral Acoustic Demonstration Center—Gulf Ecological Monitoring and Modeling (LADC-GEMM) consortium has collected passive acoustic monitoring data in the northern Gulf of Mexico since 2001. Recordings were made in 2007 near the Deepwater Horizon oil spill, which have provided a baseline for an extensive study of regional marine mammal populations in response to the disaster. Beaked whales are of particular interest as they remain one of the least understood groups of marine mammals, and relatively few abundance estimates exist. Efficient classification and clustering algorithms are demanded for mining the long-term passive acoustic data. Three algorithms using k-means, self-organizing maps, and spectral clustering are tested with various features of detected echolocation transients. Several methods are observed to effectively isolate recorded echolocation clicks of regional beaked whale species. The waveform fractal dimension is introduced as a feature for marine biosonar classification and shown to improve accuracy. A feedforward neural network classifier is also evaluated and shows performance with high accuracy under various noise conditions. [This research was made possible by a grant from The Gulf of Mexico Research Initiative. Data are publicly available through the Gulf of Mexico Research Initiative Information &amp; Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org.]

Food-Web and Ecosystem Structure of the Open-Ocean and Deep-Sea Environments of the Azores, NE Atlantic

The Marine Strategy Framework Directive intends to adopt ecosystem-based management for resources, biodiversity and habitats that puts emphasis on maintaining the health of the ecosystem alongside appropriate human use of the marine environment, for the benefit of current and future generations. Within the overall framework of ecosystem-based management, ecosystem models are tools to evaluate and gain insights in ecosystem properties. The low data availability and complexity of modelling deep-water ecosystems has limited the application of ecosystem models to few deep-water ecosystems. Here, we aim to develop an ecosystem model for the deep-sea and open ocean in the Azores exclusive economic zone with the overarching objective of characterising the food-web and ecosystem structure of the ecosystem. An ecosystem model with 45 functional groups, including a detritus group, two primary producer groups, eight invertebrate groups, 29 fish groups, three marine mammal groups, a turtle and a seabird group was built. Overall data quality measured by the pedigree index was estimated to be higher than the mean value of all published models. Therefore, the model was built with source data of an overall reasonable quality, especially considering the normally low data availability for deep-sea ecosystems. The total biomass (excluding detritus) of the modelled ecosystem for the whole area was calculated as 24.7 t km-². The mean trophic level for the total marine catch of the Azores was estimated to be 3.95, similar to the trophic level of the bathypelagic and medium-size pelagic fish. Trophic levels for the different functional groups were estimated to be similar to those obtained with stable isotopes and stomach contents analyses, with some exceptions on both ends of the trophic spectra. Omnivory indices were in general low, indicating prey speciation for the majority of the groups. Cephalopods, pelagic sharks and toothed whales were identified as groups with key ecological roles in the ecosystem. Due to concerns on the use of ecosystem models with low confidence in exploring management decisions and ecological theories, the current version of this model should only be use with caution until biomass estimates are validated with survey data or the model is fitted to time

Hematology, Serum Chemistry, and Early Hematologic Changes in Free-Ranging South American Fur Seals ( Arctocephalus australis ) at Guafo Island, Chilean Patagonia.

The establishment of clinical pathology baseline data is critical to evaluate temporal and spatial changes in marine mammal groups. Despite increased availability of studies on hematology and biochemistry of marine mammals, reference ranges are lacking for many populations, especially among fur seal species. During the austral summers of 2014 and 2015, we evaluated basic hematologic and biochemical parameters in clinically healthy, physically restrained South American fur seal ( Arctocephalus australis ) lactating females and 2-mo-old pups. We also assessed the temporal variation of hematology parameters on the pups during their first 2 mo of life. Reference ranges of lactating females were similar to those previously reported in other fur seal species. In the case of pups, reference ranges are similar to values previously reported in sea lion species. As expected, most biochemical and hematologic values differ significantly between adult females and pups. As in other otariids, South American fur seals pups are born with higher values of total red blood cells, hemoglobin, and packed cell volume, and lower numbers of total leukocytes, neutrophils, lymphocytes, and eosinophils. To the best of our knowledge, data on hematology reference values for South American fur seals has not been previously reported and is useful for continued health monitoring of this species, as well as for comparisons with other otariid groups.

Parturition process in an amphibian mammal species: new evidences in South American fur seal (Arctocephalus australis)

In mammals, the transition from a terrestrial to an aquatic environment has implied a great number of adaptations. While in terrestrial mammals the presentation of the foetus at birth is typically cephalic, in strictly aquatic mammals as cetaceans and sirenians the presentation of the foetus is mainly breech. The order Pinnipedia is the most recently evolved group of marine mammals and has an amphibian lifestyle. We document, for the first time, the parturition process in the largest breeding colony of the South American fur seal Arctocephalus australis in Uruguay and compare our results with the scarce information available for other species. The analysis of the parturition processes shows that the cephalic/breech birth ratio was 1. In this species, the presentation of the foetus did not affect the total duration of the parturition process, but the cephalic presentation implied a significantly lower duration of the stage 1 of birth, a trend that is also observed in other Otariid species. Phylogenetic reconstructions suggest that O. flavescens and E. jubatus are older than the Arctocephalus genus, having their most recent common ancestor dated between 5-5.8 mybp. Within the Arctocephalus genus, A. australis would be the most recent species (0.7 mybp). In this light, the skewed ratios of breech presentation in older otariids species may suggest a convergent adaptation toward the aquatic life. We hope this finding will promote an increase of studies aiming for a more detailed examination on the adaptive processes involved in the selection of both types of fetal presentations, and their potential effect on the survival of the pup.

Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri

Understanding the life history basis of the population dynamics of threatened species is crucial to their assessment and recovery. Within the Southern Pacific Ocean, the decline and range contraction of New Zealand sea lions (NZSLs) (Phocarctos hookeri) are an exemplary case of a major fisheries and conservation controversy. Despite the use of bycatch reduction measures, the main population of the NZSL has declined since 1998 and its vulnerability to threats is poorly understood. Here we develop a population model for the declining population of the endangered NZSL at the Auckland Islands, New Zealand (\(50^{\circ }30^{\prime }\hbox {S}, 166^{\circ }17^{\prime }\hbox {E}\)), parameterised by mark-recapture data of 2928 female NZSLs spanning 15 years from 1998 to 2012, and provide the first comprehensive analysis of NZSL population dynamics and its relationship to life history. Our model closely predicts the observed trend in population censuses of the main breeding population. We found that the population will continue to decline without effective intervention. Furthermore, we found that the population growth rate is most responsive to changes in survival of adult female NZSLs—the demographic group that is most threatened by fishery bycatch. Nevertheless, inferences about the efficacy of NZSL bycatch reduction measures are still imprecise. Combined, this could explain why the main population of NZSLs continues to decline. Our results emphasise that reliable data on bycatch reduction measures are needed, if they are to be shown to protect key demographic groups of marine mammals.

An original model of the northern Gulf of Mexico using Ecopath with Ecosim and its implications for the effects of fishing on ecosystem structure and maturity

The Gulf of Mexico (GoM) is a valuable ecosystem both socially and economically, and fisheries contribute substantially to this value. Gulf menhaden, Brevoortia patronus, support the largest fishery in the Gulf (by weight) and provide forage for marine mammals, seabirds and commercially and recreationally important fish species. Understanding the complex interactions among multiple fisheries and myriad unfished species requires tools different from those used in traditional single-species management. One such tool, Ecopath with Ecosim (EwE) is increasingly being used to construct food web models of aquatic ecosystems and to evaluate fisheries management options within a broader, ecosystem context. Here, an EwE model was developed to examine the impact of Gulf fisheries on ecosystem structure and maturity. This model builds on previously published EwE models of the GoM, and is tailored to the range and habitat of Gulf menhaden. The model presented here consists of 47 functional groups, including 4 seabird groups, 1 marine mammal group, 3 elasmobranch groups, 26 bony fish groups, 9 invertebrate groups, 3 primary producer groups and 1 detritus group. A number of different management scenarios for Gulf fisheries were modeled and the results were evaluated in terms of impacts on ecosystem maturity and development. The results of the model simulations indicated that the northern Gulf of Mexico is in an immature state (sensuOdum, 1969). Management scenarios that increased fishing pressure over time consistently resulted in a decrease in the maturity indices. In particular, we found that Gulf menhaden, as a key forage fish in the ecosystem, plays a substantial role in the structure and functioning of the ecosystem.