David Schoeman

Shark-control nets pose an entanglement risk to East Australian humpback whales during their annual northward and southward migrations between the Southern Ocean and the Coral Sea. Rates of whale entanglement exhibit seasonal and interannual variation, suggesting that an understanding of the influence of variability in the broad-scale physical environment along the migratory route would be useful in assessing risk of entanglement. This study provides a quantitative spatio-temporal analysis of the probability of whale entanglement in shark-control nets relative to the position and characteristics of the East Australian Current (EAC), the dominant oceanographic feature of the region. We use satellite-derived sea-surface temperature, and outputs from a data-assimilating ocean model, to develop multivariate, data-driven algorithms for detecting the edge of the EAC using Principal Components Analysis. We use outputs from these algorithms to model the likelihood of humpback entanglements in South-east Queensland. We find that the likelihood of entanglement increases when the EAC edge is locally less structured and closer to shore in the vicinity of the corresponding net, or when the EAC is well resolved over the entire study domain. Our results suggest that migrating humpbacks use the gradient in physical characteristics that marks the EAC inner edge as a navigational aid. Thus, when the EAC inner edge encroaches on the coast, the whales' migration range is compressed into nearshore waters, increasing the risk of entanglement. Our findings can help predict periods of elevated entanglement risk, which could underpin a more data-driven approach to the management of shark-control programs, and other activities that involve static fishing gear.

In polyandrous species, sexual selection extends beyond mating competition to selection for egg fertilization. As a result, the degree to which factors influencing mating success impact overall reproductive success becomes variable. Here, we used a longitudinal behavioural and genetic dataset for a population of eastern water dragons (Intellagama lesueurii) to investigate the degree to which male dominance, a pre-mating selection trait, influences overall reproductive success, measured as the number of surviving offspring. Moreover, we examine the interactive effects with a genetic trait, individual inbreeding, known to influence the reproductive success of males in this species. We found fitness benefits of male dominance, measured as body size and frequency of dominance behaviours displayed. However, individuals' propensity to display dominance behaviours had mixed effects, depending on the degree of inbreeding. While inbred males benefited from frequent displays, highly outbred males exhibited better reproductive outputs when displaying to a lesser extent. Given that outbred males have enhanced reproductive success in this species, the costs of displaying dominance behaviours may outweigh the benefits. Overall, our results demonstrate the fitness benefits of dominance in a polyandrous lizard, and suggest that these are modulated by an independent genetic trait. Our results may contribute to explaining the presence of alternative mating tactics in this species, owing to the variability in net fitness benefits of dominance. Our findings also reveal the challenges associated with investigating fitness traits in isolation, which may undermine the validity of results when important interactions are ignored.

Climate change is increasing the frequency and severity of marine heatwaves. A recent extreme warming event (2014-2016) of unprecedented magnitude and duration in the California Current System allowed us to evaluate the response of the kelp forest community near its southern (warm) distribution limit. We obtained sea surface temperatures for the northern Pacific of Baja California, Mexico, and collected kelp forest community data at three islands, before and after the warming event. The warming was the most intense and persistent event observed to date, with low-pass anomalies 1°C warmer than the previous extremes during the 1982-1984 and 1997-1998 El Niños. The period between 2014-2017 accounted for ~50% of marine heatwaves days in the past 37 years, with the highest maximum temperature intensities peaking at 5.9°C above average temperatures for the period. We found significant declines in the number of Macrocystis pyrifera individuals, except at the northernmost island, and corresponding declines in the number of fronds per kelp individual. We also found significant changes in the community structure associated with the kelp beds: half of the fish and invertebrate species disappeared after the marine heatwaves, species with warmer affinities appeared or increased their abundance, and introduced algae, previously absent, appeared at all islands. Changes in subcanopy and understory algal assemblages were also evident; however, the response varied among islands. These results suggest that the effect of global warming can be more apparent in sensitive species, such as sessile invertebrates, and that warming-related impacts have the potential to facilitate the establishment of tropical and invasive species.

Environmental Impact Assessments (EIAs) are at the frontline of balancing economic, societal and environmental needs. With the world expected to invest around $90 trillion in infrastructure in the next 15 years, resulting in more new infrastructure than is currently in existence globally (Jan Corfee-Morlot et al., 2016), there has never been a more critical time for EIAs to get it right. Yet even in Australia, a wealthy, economically and politically stable nation with multiple environmental laws and comparatively effective governance, environmental legislation has failed to effectively protect wildlife (McDonald et al., 2015). By and large, the same story holds true worldwide (Laurance, 2018a). For some species, current failings to halt their trajectory toward extinction have been directly linked to inappropriate EIAs (Reside et al., 2019).

As ocean temperatures rise, species distributions are tracking towards historically cooler regions in line with their thermal affinity1,2. However, different responses of species to warming and changed species interactions make predicting biodiversity redistribution and relative abundance a challenge3,4. Here, we use three decades of fish and plankton survey data to assess how warming changes the relative dominance of warm-affinity and cold-affinity species5,6. Regions with stable temperatures (for example, the Northeast Pacific and Gulf of Mexico) show little change in dominance structure, while areas with warming (for example, the North Atlantic) see strong shifts towards warm-water species dominance. Importantly, communities whose species pools had diverse thermal affinities and a narrower range of thermal tolerance showed greater sensitivity, as anticipated from simulations. The composition of fish communities changed less than expected in regions with strong temperature depth gradients. There, species track temperatures by moving deeper2,7, rather than horizontally, analogous to elevation shifts in land plants8. Temperature thus emerges as a fundamental driver for change in marine systems, with predictable restructuring of communities in the most rapidly warming areas using metrics based on species thermal affinities. The ready and predictable dominance shifts suggest a strong prognosis of resilience to climate change for these communities.