AI Noteworthy (formerly Hot Topics) 2021

Noteworthy (formerly Hot Topics) (pdf)

This section replaces the previously-named Hot Topics. We include information here that is deemed of relevance to ecosystem considerations of fisheries managers, but does not fit our typical indicator format. Information included here is often new, a one-time event, qualitative, or some other type of non-standard ecosystem indicator.

Mercury in Aleutian Islands food webs

Relatively high total mercury concentrations ([THg]) have been identified in over 25% of the Steller sea lion pups sampled to date in the western and central Aleutian Islands rookeries (Rea et al., 2013, 2020, 2021). These young rookery pups were exposed to mercury during in utero development, a particularly vulnerable time during fetal neurological development. Fetal exposure to mercury has been documented in harbor seals to cause abnormal neurological symptoms (Van Hoomissen et al., 2015), including decreased response to tactile stimuli and decreased movement (Lian et al., 2020). This indicates that adult female Steller sea lions ingested mercury tainted fish or cephalopod prey (Tollit et al., 2017; Scherer et al., 2015; Doll et al., 2018) during the mid- or late-gestation period that passed to pups across the placenta. Pups can be further exposed to additional low levels of mercury through ingestion of maternal milk. Unlike persistent organic pollutants which associate mostly with fats, mercury has a higher affinity with protein and thus fetal exposure is much higher than during the nursing period.

Mercury has been shown to negatively impact health, survival, and reproduction in other wildlife species (Wolfe et al., 1998; O’Hare and Hart, 2018). Recent research has shown evidence of adverse toxicological effect in SSL pups at the concentrations of mercury found in some pups in the Aleutian Islands. Pups with total mercury concentrations above 0.1 µg/g wet weight in whole blood showed decreased immune function (e.g., haptoglobin response Kennedy et al. 2019). Pups with elevated total mercury concentrations (and thus lower selenium to mercury molar ratios) also had poor antioxidant function (Lian et al., 2021) which could lead to tissue oxidative damage when free radicals are produced in peripheral muscles and internal organs (like liver, kidney and heart) during active breath-hold diving. Methylmercury exposure has also been shown to impact the immune system through impacting the proliferation of white blood cells both in vitro (e.g., exposure of blood cells in a controlled laboratory setting Levin et al. 2020) and in vivo (e.g., response of cells to natural exposure in rookery pups Keogh et al. In Review).

The concentrations of mercury and the proportion of pups with mercury concentrations above this lower toxicological level of concern have increased significantly over the past 10 years. Rea et al. (2021) found a broad range of [THg] (2.55–73.74 µg/g dw) was found in lanugo (natal hair) samples from pups sampled at Agattu Island in June of 2011, 2012, 2013, 2015, 2017, 2018, and 2019 (n=339).A significant increase in median [THg] in the lanugo of pups was identified over this brief period from 8.005 µg/g in 2011 to 17.275 µg/g in 2019 (Kruskal-Wallis H=41.24, p<0.001). The proportion of pups sampled on Agattu Island with lanugo [THg] above 20 µg/g THg (a published threshold of adverse effect of mercury in pinnipeds) increased more than twofold during this time period from 20.6% in 2011 to 46.4% in 2019. The proportion of pups at high risk for adverse effects increased at a rate of 3.7% per year. These biologically significant increases in [THg] accumulated through maternal diet are particularly concerning due to the short, intra-decadal scale of the escalation and the consistent rate of increase of proportion of pups at risk.

Higher median total mercury concentrations in lanugo of young pups have also been measured on rookeries that continue to decline in population and that show lower total selenium (TSe) to THg molar ratios in pup blood (Rea et al., 2020). As an essential antioxidant and modulator of Hg toxicosis it is important to interpret THg relative to TSe. This research on Steller sea lion mercury concentrations has been undertaken in collaboration with NOAA and colleagues at Texas A&M University, and we eagerly await the possibility to assess continuing trends once the pandemic abates and field sampling is once again possible.More limited sampling of harbor seals in the Aleutian Islands suggests that phocid seals foraging from the same island location as Steller sea lions can have a similar range of total mercury concentrations in their hair, and also be at risk for toxic effects (Rea et al., 2017).

Other studies are currently underway to understand movement of mercury through the food web to help identify potential sources and to understand whether these same trends of increasing mercury concentrations are apparent in fish prey species sampled in the Aleutian Islands. Ocean Peace Inc. have been an important research donor and collaborator since 2013, providing fish sampled from commercial trawls and supporting student research to measure mercury and stable isotopes in Aleutian fish and cephalopods. This research has shown that mercury concentrations in several fish species are significantly higher in the western Aleutian Islands compared to fish sampled to the east (Cyr et al., 2019). This concurs with prior research on seabirds which showed higher levels of mercury in towards the west in glaucous-winged gull and northern fulmars in Buldir Island (Ricca et al., 2008). More recent collections now enable analysis of whether there have been increases in mercury in these fish species over the past decade. A new collaboration with the US Fish and Wildlife Service has also provided a large set of invertebrate species from the central and western Aleutian Islands. This will allow measurement of mercury and selenium in more sessile, nearshore organisms. that will assist in determining if there are discrete regions within the Aleutian Islands that have higher mercury concentrations (and potential toxicologic risk) that should be the focus of future research.

Contributed by: Lorrie Rea Marine Ecotoxicology and Trophic Assessment Laboratory (METAL), University of Alaska, Fairbanks

Plastics in the Aleutian Islands

Plastics derived contaminants, phtalates, were detected in 115 seabirds tested with concentrations varying from 3.64–539.64 ng/g. While phthalates did not vary geographically, diving plankton- feeders showed significantly higher concentrations compared to diving fish, surface fish, and op- portunistic feeders. Species sampled included: diving fish-feeders, common murre, horned and tuftedpPuffins, pelagic and red-faced cormorants and pigeon guillemots; two species of surface fish-feeders: black-legged kittiwakes and northern fulmars; one species of diving plankton-feeder: crested auklet; and one species of opportunistic feeder: glaucous-winged gulls. Plastic particles were detected in 36.5% of subsampled stomachs (n = 74), suggesting plastic ingestion as a poten- tial route of phthalate exposure (Padula et al., 2020). While harmful levels of phtalates wre not assessed, Lavers et al. (2019) studied the sublethal effects of ingested plastic in flesh-footed shear- waters and found the presence of plastic had a significant adverse effects on seabird morphometrics, blood calcium levels, and were positively correlated with the concentration of uric acid, cholesterol, and amylase. These sublethal effects of ingesting plastic show seabirds may still experience adverse consequences despite being apparently healthy. While ingesting marine debris can lead to mortality it is not the leading cause (Roman et al., 2019). Out of 1733 seabirds examined, 557 (32.1%) had ingested marine debris, and 22 were determined to have died from debris ingestion. The study found ingesting one item has a 20.4% chance of lifetime mortality, while 93 items increase the chance to 100%. When mortality by plastic ingestion does occur, the leading cause of death was found to be obstruction of the gastro-intestinal tract, with balloons32 times more likely to result in death than ingesting hard plastic Roman et al. (2019). Regional variability in the amount of plastics ingested depends both on the foraging ecology of the species as well as the areas in which they are foraging.

Contributed by: Ivonne Ortiz Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington, Seattle, WA.