A three year study of metal levels in skin biopsies of whales in the Gulf of Mexico after the Deepwater Horizon oil crisis.

In response to the explosion of the Deepwater Horizon and the massive release of oil that followed, we conducted three annual research voyages to investigate how the oil spill would impact the marine offshore environment. Most investigations into the ecological and toxicological impacts of the Deepwater Horizon Oil crisis have mainly focused on the fate of the oil and dispersants, but few have considered the release of metals into the environment. From studies of previous oil spills, other marine oil industries, and analyses of oil compositions, it is evident that metals are frequently encountered. Several metals have been reported in the MC252 oil from the Deepwater Horizon oil spill, including the nonessential metals aluminum, arsenic, chromium, nickel, and lead; genotoxic metals, such as these are able to damage DNA and can bioaccumulate in organisms resulting in persistent exposure. In the Gulf of Mexico, whales are the apex species; hence we collected skin biopsies from sperm whales (Physeter macrocephalus), short-finned pilot whales (Globicephala macrorhynchus), and Bryde's whales (Balaenoptera edeni). The results from our three-year study of monitoring metal levels in whale skin show (1) genotoxic metals at concentrations higher than global averages previously reported and (2) patterns for MC252-relevant metal concentrations decreasing with time from the oil spill.

Critical Decline of the Eastern Caribbean Sperm Whale Population.

Sperm whale (Physeter macrocephalus) populations were expected to rebuild following the end of commercial whaling. We document the decline of the population in the eastern Caribbean by tracing demographic changes of well-studied social units. We address hypotheses that, over a ten-year period of dedicated effort (2005-2015), unit size, numbers of calves and/or calving rates have each declined. Across 16 units, the number of adults decreased in 12 units, increased in two, and showed no change in two. The number of adults per unit decreased at -0.195 individuals/yr (95% CI: -0.080 to -0.310; P = 0.001). The number of calves also declined, but the decline was not significant. This negative trend of -4.5% per year in unit size started in about 2010, with numbers being fairly stable until then. There are several natural and anthropogenic threats, but no well-substantiated cause for the decline.

Acoustically derived growth rates of sperm whales (Physeter macrocephalus) in Kaikoura, New Zealand.

A non-invasive acoustic method for measuring the growth of sperm whales was developed based on estimating the length of individuals by measuring the inter-pulse interval (IPI) of their clicks. Most prior knowledge of growth in male sperm whales has come from from fitting growth curves to length data gained from whaling. Recordings made at Kaikoura, New Zealand, were used to estimate the length and growth of 32 photographically identified, resident whales that have been recorded repeatedly between 1991 and 2009. All whales recorded more than six months apart (n = 30) showed an increase in IPI. Using established relationships between IPI and total length, it was found that the average growth rate in the Kaikoura population is lower, especially for smaller whales (13-14.5 m), than that derived from historical whaling data from other populations. This difference may be due to ecological differences among populations but might also reflect upward bias in measurements gained in whaling. The ability to track growth of individuals through time is only possible via non-lethal means and offers a fundamentally different kind of data because differences among individuals can be measured.

Global mercury and selenium concentrations in skin from free-ranging sperm whales (Physeter macrocephalus).

Pollution of the ocean by mercury (Hg) is a global concern. Hg persists, bioaccumulates and is toxic putting high trophic consumers at risk. The sperm whale (Physeter macrocephalus), is a sentinel of ocean health due to its wide distribution, longevity and high trophic level. Our aim was to survey Hg concentrations worldwide in the skin of free-ranging sperm whales considering region, gender and age. Samples were collected from 343 whales in 17 regions during the voyage of the research vessel, Odyssey, between 1999 and 2005. Skin was analyzed for total Hg and detected in all but three samples with a global mean of 2.5±0.1 µg g(-1) ranging from 0.1 to 16.0 µg g(-1). The Mediterranean Sea had the highest regional mean with 6.1 µg g(-1) followed by Australia with 3.5 µg g(-1). Considering gender, females and males did not have significantly different global Hg concentrations. The variation among regions for females was significantly different with highest levels in the Mediterranean and lowest in Sri Lanka; however, males were not significantly different among regions. Considering age in males, adults and subadults did not have significantly different Hg concentrations, and were not significantly different among regions. The toxic effects of these Hg concentrations are uncertain. Selenium (Se), an essential element, antagonizes Hg at equimolar amounts. We measured total Se concentrations and found detectable levels in all samples with a global mean of 33.1±1.1 µg g(-1) ranging from 2.5 to 179 µg g(-1). Se concentrations were found to be several fold higher than Hg concentrations with the average Se:Hg molar ratio being 59:1 and no correlation between the two elements. It is possible Hg is being detoxified in the skin by another mechanism. These data provide the first global analysis of Hg and Se concentrations in a free-ranging cetacean.