Sean A. Hayes

Marine survival of steelhead (Oncorhynchus mykiss) enhanced by a seasonally closed estuary

To investigate the role that estuaries play in the survival of steelhead, Oncorhynchus mykiss, we compared juve- nile size at ocean entry with back-calculated measures of size at ocean entry for returning adults in Scott Creek, a repre- sentative California coastal stream. During the annual spring emigration, the largest smolts (>150 mm fork length (FL)) move directly to sea, while some smaller smolts remain in the estuary until sandbar formation creates a closed freshwater lagoon. High growth rates in the estuary throughout the summer result in a near doubling of fork length from the time of estuary entry (mean FL of spring migrants = 102.2 mm; mean FL of fall lagoon resident = 195.9 mm). Analysis of the scale morphology of returning adult steelhead indicates that there is strong size-dependent mortality at sea, with estuary- reared steelhead showing a large survival advantage, comprising between 87% and 95.5% (based on tag returns and scale analysis, respectively) of the returning adult population despite being between 8% and 48% of the annual downstream mi- grating population. Although the estuary forms less than 5% of the watershed area, it is critical nursery habitat, and steel- head population persistence in southern margin ecosystems may well depend upon healthy estuaries.

Over the Falls? Rapid Evolution of Ecotypic Differentiation in Steelhead/Rainbow Trout (Oncorhynchus mykiss)

Adaptation to novel habitats and phenotypic plasticity can be counteracting forces in evolution, but both are key characteristics of the life history of steelhead/rainbow trout (Oncorhynchus mykiss). Anadromous steelhead reproduce in freshwater river systems and small coastal streams but grow and mature in the ocean. Resident rainbow trout, either sympatric with steelhead or isolated above barrier dams or waterfalls, represent an alternative life-history form that lives entirely in freshwater. We analyzed population genetic data from 1486 anadromous and resident O. mykiss from a small stream in coastal California with multiple barrier waterfalls. Based on data from 18 highly variable microsatellite loci (He = 0.68), we conclude that the resident population above one barrier, Big Creek Falls, is the result of a recent anthropogenic introduction from the anadromous population of O. mykiss below the falls. Furthermore, fish from this above-barrier population occasionally descend over the falls and have established a genetically differentiated below-barrier subpopulation at the base of the falls, which appears to remain reproductively isolated from their now-sympatric anadromous ancestors. These results support a hypothesis of rapid evolution of a purely resident life history in the above-barrier population in response to strong selection against downstream movement.

Steelhead Growth in a Small Central California Watershed: Upstream and Estuarine Rearing Patterns

We monitored growth and life history pathways of juvenile steelhead Oncorhynchus mykiss and compared growth rates between the upper watershed and estuary in Scott Creek, a typical California coastal stream. Growth in the upper watershed was approximately linear from May to December for age-0 fish. For passive integrated transponder (PIT) tagged, age-1þ fish, growth transitioned to a cyclic pattern, peaking at 0.2% per day during February-April, when maximum flows and temperatures of 7-128C occurred. Growth of PIT-tagged fish then slowed during August-September (0.01% per day), when temperatures were 14-188C and flows were low. During each spring, smolts (mean fork length (FL) 6 SE ¼ 98.0 6 1.2 mm) and fry migrated to the estuary; some fish remained there during summer-fall as low flows and waves resulted in seasonal sandbar formation, which created a warm lagoon and restricted access to the ocean. Growth in the estuary-lagoon was much higher (0.2-0.8% per day at 15-248C). Our data suggest the existence of three juvenile life history pathways: upper-watershed rearing, estuary-lagoon rearing, and combined upper- watershed and estuary-lagoon rearing. We present a model based upon the above data that reports size at age for each juvenile life history type. The majority of fish reaching typical steelhead ocean entry sizes (;150- 250 mm FL; age 0.8-3.0) were estuary-lagoon reared, which indicates a disproportionate contribution of this habitat type to survival of Scott Creek steelhead. In contrast, steelhead from higher latitudes rear in tributaries during summer, taking several years to attain ocean entry size.

The effect of a Low-Frequency Sound Source (Acoustic thermometry of the Ocean Climate) on the Diving behavior of Juvenile Northern Elephant Seals, Mirounga Angustirostris

Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.

A New Low-Cost Instream Antenna System for Tracking Passive Integrated Transponder (PIT)-Tagged Fish in Small Streams

Abstract We present a new, low-cost, low-power, half/full-duplex passive integrated transponder (PIT) tag interrogation antenna for use in detecting fish movements in small streams. New technology by Allflex-USA allowed us to develop a reading system with an antenna 279.4 cm wide × 60.9 cm high that reads both common tag types used in fisheries today for about US

Size at Release, Size-Selective Mortality, and Age of Maturity of Willamette River Hatchery Yearling Chinook Salmon

1,000. An instream antenna of this size and price makes high-resolution tracking of fish movement in small streams feasible where cost and tag-type restrictions were prohibitive. For evaluation, we placed the antenna upstream of a small estuary on the central California coast to observe the diel movements of juvenile steelhead Oncorhynchus mykiss between the estuary and upstream habitats in both spring and fall months.

Evaluating the function of the male harbour seal, Phoca vitulina, roar through playback experiments

Abstract We analyzed scales from returning Willamette River yearling Chinook salmon Oncorhynchus tshawytscha to explore the effects of size at release on subsequent adult returns. We tested the hypothesis that survival to adulthood is independent of size at ocean entry for yearling Chinook salmon. Significant size-selective mortality, indicated by a larger size at ocean entry among surviving adults than among all released juveniles, was observed for Chinook salmon released in 2002–2004 but not for those released in 2005. Juvenile Chinook salmon released in 2002–2004 that entered the ocean at less than 150 mm in fork length were underrepresented in the returning adult populations. We also investigated the relationships between age at maturity and size at ocean entry, timing of release, circulus spacing, and size at the end of the first ocean year. We observed significant differences in fork length at the end of the first ocean winter among returning age-4, -5, and -6 Chinook salmon; the younger returning f...

Patterns in the vocalizations of male harbor seals

Abstract The aim of this study was to evaluate the role of vocalizations produced during the breeding season by the male harbour seal, an aquatically breeding pinniped. During the spring of 1999, playback experiments were conducted at eight locations in Elkhorn Slough, California, U.S.A. Through an underwater speaker, we presented male harbour seals with three acoustic stimuli: a long-duration, low-frequency roar (LL), a short-duration, high-frequency roar (SH) and amplified water noise (control). Male responses to the playback boat were characterized by increased approach rates and aggressive flipper slapping during 62.5% of SH sessions ( N =8), 25% of LL sessions ( N =8) and 0% of control sessions ( N =8). No more than one identifiable seal responded during each playback location. We observed no responses by female harbour seals to playbacks. We conclude from these experiments that territorial male harbour seals use roars given by intruders to locate and challenge intruders.

Should I Stay or Should I Go? The Influence of Genetic Origin on Emigration Behavior and Physiology of Resident and Anadromous Juvenile Oncorhynchus mykiss

Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects.

An inexpensive passive acoustic system for recording and localizing wild animal sounds

Abstract We investigated the interaction among genetically identified origin, behavioral tendency to emigrate, and Na+, K+-ATPase enzyme activity in recently diverged subpopulations of resident (above-barrier) rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) in Scott Creek, California. Genetic assignment tests found that the frequency of resident and anadromous origin fish varied by sampling location within the watershed. Individuals immediately below barriers assigned to both above-barrier (37%) and anadromous (63%) subpopulations, and distinct differences in size and age were observed. However, the majority of downstream migration behavior occurred in fish of anadromous ancestry, which represented 97% of the fish sampled as outmigrating smolts. Nonmigratory fish of both life history types and origins typically had low Na+, K+-ATPase activity levels throughout most of the year, but significantly elevated levels were observed in individuals from both groups during the spring smol...