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Abstract I describe my path through a series of opportunities that provided stepping stones from childhood years in the landlocked US Midwest to a 45-year-long career focused on cetacean behaviour and ecology. My early interest in the ocean and dolphins led me to switch from majoring in journalism to biology during my undergraduate years. While pursuing a master’s degree focused on bioacoustics, I was employed as a contract scientist with the US Navy’s marine mammal laboratory. During 20 years there, my work ranged from dolphin calling behaviour to marine mammal distribution in Alaskan waters, culminating in a Ph.D. dissertation on cetacean habitats in the Alaskan Arctic. Subsequently, I enjoyed a 20-year career with the US NOAA National Marine Fisheries Service. There, I developed and advanced the idea that marine mammals can act as sentinels of ocean variability. To interpret the messages that marine mammals convey about the ocean, we must broaden science discourse to include Indigenous Knowledge and lessons from the experiences of people whose livelihoods depend on the sea. My advice to students and young professionals is to follow your passion while seeking the perspectives of colleagues from a variety of disciplines and people from all cultures and backgrounds. Coupledmore »with a healthy dose of luck, this approach worked for me.« less

Abstract Experiments examining fish sensitivities to future oceanic CO2 levels have greatly expanded over past decades and identified many potentially affected traits. Curiously, data on reproductive trait responses to high CO2 are still scarce, despite their strong link to Darwinian fitness and thus to population vulnerability to ocean acidification. We conducted two rearing experiments on the first broadcast-spawning marine fish model (Atlantic silverside, Menidia menidia) to examine how long-term and novel whole life-cycle exposures to predicted future CO2 levels (∼2,000 µatm) affect laboratory spawning, temperature-specific reproductive investment, fecundity, and size distributions of maturing oocytes. At low temperatures (17°C), female body size and therefore potential fecundity (FPot, oocytes/female) slightly increased with CO2, while relative fecundity (FRel, oocytes/g female) remained unaffected. At high temperatures (24°C), high CO2 substantially reduced both FPot (−19%) and FRel (−28%) relative to control treatments. Irrespective of CO2, females at 24°C grew larger and heavier than those at 17°C, and although larger females produced larger oocytes at some developmental stages, they also had lower gonadosomatic indices and lower FRel. Our findings contrast with most previous studies and thus highlight the need to investigate reproductive impacts of increasing CO2 on multiple fish species with contrasting life history strategies.

Ocean acidification may impact the fitness of marine fish, however, studies reporting neutral to moderate effects have mostly performed short-term exposures to elevated CO2, whereas longer-term studies across life stages are still scarce. We performed a CO2 exposure experiment, in which a large number (n > 2200) of Atlantic silverside Menidia menidia offspring from wild spawners were reared for 135 days through their embryonic, larval, and juvenile stages under control (500 µatm) and high CO2 conditions (2300 µatm). Although survival was high across treatments, subtle but significant differences in length, weight, condition factor and fatty acid (FA) composition were observed. On average, fish from the acidified treatment were 4% shorter and weighed 6% less, but expressed a higher condition factor than control juveniles. In addition, the metrics of length and weight distributions differed significantly, with juveniles from the high CO2 treatment occupying more extreme size classes and the length distribution shifting to a positive kurtosis. Six of twenty-seven FAs differed significantly between treatments. Our results suggest that high CO2 conditions alter long-term growth in M. menidia, particularly in the absence of excess food. It remains to be shown whether and how these differences will impact fish populations in the wild facing size-selectivemore »predation and seasonally varying prey abundance.« less