Jayson M. Semmens

Elevated trace element concentrations, such as those found within the waters of Macquarie Harbour, Tasmania, Australia, are known to cause a suite of deleterious effects on the functioning of organisms. Consequently, it is important that the accumulation of these pollutants be monitored within aquatic food chains. The Maugean skate (Zearaja maugeana), an endangered species of elasmobranch, resides only within the polluted waters of Macquarie Harbour. Consequently, the extent of trace element accumulation within its tissues should be monitored. The current study aimed to quantify trace element concentrations in Maugean skate muscle with the use of non-lethal sampling and compare these concentrations with those determined in previous studies. Trace element concentrations were determined within muscle samples with the use of solution Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis. The current study revealed Chromium, Cobalt, Copper, Lead, and Strontium concentrations higher than that previously described within the muscle tissue of the Maugean skate. The concentrations of these elements were also notably higher than those typically found in elasmobranchs inhabiting southern Australian waters. Chromium, Cobalt, Copper, and Lead concentrations determined herein suggested the potential for toxicity effects to have been experienced by the Maugean skate. The biopsy punch methodology described herein provided an effective non-lethal toolset to assess trace element accumulation within Maugean skate muscle. It is recommended that trace element accumulation within the skate continue to be monitored, and its potential effects on the ecological functioning and reproductive success of the species be investigated.

Cruising speed is a key factor affecting prey-search efficiency and migration range in continuously swimming animals. Tunas and lamnid sharks (e.g., white sharks) have convergently evolved traits for high-speed cruising, including the ability to maintain slow-twitch, aerobic red muscle (RM) warmer than ambient water, known as RM endothermy. Despite their well-known high cruising speeds, kinematic features underlying their elevated speeds remain unclear. Swim speed is the product of tailbeat frequency (TBF; Hz) and stride length (SL, the absolute distance traveled per tailbeat; m). RM endothermy is expected to elevate TBF by enhancing muscle contraction performance. Furthermore, within RM-endothermic fishes, tunas and lamnid sharks may exhibit distinct kinematic features because of differences in caudal fin morphology and tailbeat amplitude. Here, we compiled kinematic parameters from 20 fish species, including five RM-endothermic species, measured in the wild using animal-borne sensors. Comparative analyses showed that, for a given body mass and water temperature, RM-endothermic fishes exhibited 1.9 times higher cruising speed and TBF than ectothermic fishes, while SL remained similar. Within RM-endothermic fishes, tunas exhibited 2.3 times higher TBF than similar-sized lamnid sharks, whereas lamnid sharks showed 1.7 times longer SL than similar-sized tunas. These results indicate that RM endothermy is generally associated with higher TBF, while significant kinematic differences remain between tunas and lamnid sharks. This divergence may be partly explained by the greater caudal fin area and tailbeat amplitude in lamnid sharks. It may also reflect contrasting skeletal types of teleosts and elasmobranchs, which potentially influence body stiffness and swimming kinematics.

The school shark, Galeorhinus galeus (Linnaeus, 1758), is the only extant species within its genus and is widely distributed in benthopelagic habitats of temperate coastal regions. Fishing pressure has caused global population declines by more than 80%, resulting in the species being listed as Critically Endangered. Here, we present the first chromosome-level, haplotype-phased reference genome assemblies for G. galeus , including assemblies of both male and female individuals. The 4.81 Gbp male genome was assembled from PacBio HiFi and Dovetail Omni-C proximity ligation sequencing data, and the 4.52 Gbp female genome was assembled from PacBio HiFi data scaffolded via homology to the curated male genome. Both genomes are >92% BUSCO complete and contain ~60–63% repeat content. Analysis of methylation levels and single nucleotide polymorphism density across chromosomes revealed several regions where high SNP density co-located with relative hypomethylation, indicating a reciprocal relationship between these two features. These genomes are a valuable resource enabling future genomic studies to inform population management and conservation strategies for this Critically Endangered species.

Group living determines how animals interact with others and their habitat. Elephant fish ( Callorhinchus milii ) are chimaeras (Class Chondrichthyes, subclass Holocephali) that migrate to coastal waters for reproduction throughout its southern Australian range. However, there is limited information about how they co-utilize these areas. This study used social network analysis (SNA) and passive acoustic monitoring data to examine associations between adult elephant fish in an estuary in southeastern Tasmania, Australia (42°53.710′S 147°34.228′E), specifically Pitt Water and Frederick Henry Bay (FHB) from January 2012 to December 2013. The influence of sex on the social structure was also investigated. As a result, two distinct groups of animals (clusters) were found across both years: a resident female cluster that remained in the upper estuary (UP) and a mixed-sex group whose movements varied seasonally. These clusters formed a cohesive community, with the female cluster potentially playing a critical role in connecting the population members. The mixed-sex group split into temporary aggregations, a so-called fission-fusion society that relies on seasonal reproductive patterns. Furthermore, by investigating all the individuals (including both clusters), spatial sex segregation was evident. The suitable conditions of the upper part of the estuary for egg-laying and the mating dynamics may shape the association structure observed. These findings highlight the importance of these essential habitats for elephant fish reproduction and emphasize the need for management strategies that incorporate space co-utilization patterns, address sex-based segregation, and recognize the role of females in maintaining social structure to ensure population stability and connectivity.

The recent Kunming-Montreal Global Biodiversity Framework (GBF) sets ambitious goals but no clear pathway for how zero loss of important biodiversity areas and halting human-induced extinction of threatened species will be achieved. We assembled a multi-taxa tracking dataset (11 million geopositions from 15,845 tracked individuals across 121 species) to provide a global assessment of space use of highly mobile marine megafauna, showing that 63% of the area that they cover is used 80% of the time as important migratory corridors or residence areas. The GBF 30% threshold (Target 3) will be insufficient for marine megafauna’s effective conservation, leaving important areas exposed to major anthropogenic threats. Coupling area protection with mitigation strategies (e.g., fishing regulation, wildlife-traffic separation) will be essential to reach international goals and conserve biodiversity.

Body-size relationships between predators and prey exhibit remarkable diversity. However, the assumption that predators typically consume proportionally smaller prey often underlies size-dependent predation in ecosystem models. In reality, some animals can consume larger prey or exhibit limited changes in prey size as they grow larger themselves. These distinct predator–prey size relationships challenge the conventional assumptions of traditional size-based models. Cephalopods, with their diverse feeding behaviours and life histories, offer an excellent case study to investigate the impact of greater biological realism in predator–prey size relationships on energy flow within a size-structured ecosystem model. By categorizing cephalopods into high and low-activity groups, in line with empirically derived, distinct predator–prey size relationships, we found that incorporating greater biological realism in size-based feeding reduced ecosystem biomass and production, while simultaneously increasing biomass stability and turnover. Our results have broad implications for ecosystem modelling, since distinct predator–prey size relationships extend beyond cephalopods, encompassing a wide array of major taxonomic groups from filter-feeding fishes to baleen whales. Incorporating a diversity of size-based feeding in food web models can enhance their ecological and predictive accuracy when studying ecosystem dynamics.