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Title: Disentangling the effects of fishing and environmental forcing on demographic variation in an exploited species
Description: Species targeted by fishing often recover in abundance and size within marine protected areas (MPAs) resulting in increased reproductive potential. However, in some situations, concomitant changes in the abundance of predators, competitors, or prey within MPAs, or strong gradients in the surrounding environmental seascape may counteract the purported benefits making it more difficult to predict how species will respond to protection. We used a network of MPAs in California, spanning a large temperature gradient, to investigate the drivers of demographic variability in the commercially important red sea urchin Mesocentrotus franciscanus. We investigated how demographic metrics varied geographically in response to protection, temperature, and the main sea urchin resource, the giant kelp Macrocystis pyrifera. We found significant conservation benefits to this fished sea urchin within MPAs designated six years prior to the beginning of this study. Within MPAs, red sea urchins were generally larger resulting in greater adult biomass density and reproductive biomass density. In addition, kelp density was an important explanatory variable of all red sea urchin demographic traits examined (adult size, gonadosomatic index [GSI], density, adult biomass density, and reproductive biomass density). Kelp density was positively correlated with red sea urchin GSI and adult size, but the relationships with density, adult biomass density, and reproductive biomass density were complex and the directionality changed depending on the region (or environmental setting) examined. Our results demonstrate that kelp, red sea urchin reproduction, and the effects of spatial management on demographic processes are tightly coupled with the oceanographic regime. © 2017 Elsevier Ltd
Author: Teck, Lorda, Shears, Bell, Cornejo-Donoso, Caselle, Hamilton, Gaines

Title: Dietary niche expansion of a kelp forest predator recovering from intense commercial exploitation
Description: Marine ecosystems are increasingly at risk from overexploitation and fisheries collapse. As managers implement recovery plans, shifts in species interactions may occur broadly with potential consequences for ecosystem structure and function. In kelp forests off San Nicolas Island, California, USA, we describe striking changes in size structure and life history traits (e.g., size at maturation and sex change) of a heavily fished, ecologically important predator, the California sheephead (Semicossyphus pulcher). These changes occurred in two phases: (1) after intense commercial fishery exploitation in the late 1990s and (2) following recovery in the late 2000s, nearly a decade after management intervention. Using gut contents and stable-isotope values of sheephead and their prey, we found evidence for a dietary niche expansion upon recovery of population size structure to include increased consumption of sea urchins and other mobile invertebrate grazers by larger sized fish. By examining historical diet data and a time series of benthic community composition, we conclude that changes in dietary niche breadth are more likely due to the recovery of size structure from fishing than major shifts in prey availability. Size-dependent predator-prey interactions may have ecosystem consequences and management measures that preserve or restore size structure, and therefore historical trophic roles of key predators, could be vital for maintaining kelp forest ecosystem health. © 2014 by the Ecological Society of America., Fish and Fisheries
Author: Hamilton, Newsome, Caselle

Title: First quantification of subtidal community structure at Tristan da Cunha Islands in the remote South Atlantic from kelp forests to the deep sea
Description: Tristan da Cunha Islands, an archipelago of four rocky volcanic islands situated in the South Atlantic Ocean and part of the United Kingdom Overseas Territories (UKOTs), present a rare example of a relatively unimpacted temperate marine ecosystem. We conducted the first quantitative surveys of nearshore kelp forests, offshore pelagic waters and deep sea habitats. Kelp forests had very low biodiversity and species richness, but high biomass and abundance of those species present. Spatial variation in assemblage structure for both nearshore fish and invertebrates/algae was greatest between the three northern islands and the southern island of Gough, where sea temperatures were on average 3-4o colder. Despite a lobster fishery that provides the bulk of the income to the Tristan islands, lobster abundance and biomass are comparable to or greater than many Marine Protected Areas in other parts of the world. Pelagic camera surveys documented a rich biodiversity offshore, including large numbers of juvenile blue sharks, Prionace glauca. Species richness and abundance in the deep sea is positively related to hard rocky substrate and biogenic habitats such as sea pens, crinoids, whip corals, and gorgonians were present at 40% of the deep camera deployments. We observed distinct differences in the deep fish community above and below ~750 m depth. Concurrent oceanographic sampling showed a discontinuity in temperature and salinity at this depth. While currently healthy, Tristan's marine ecosystem is not without potential threats: shipping traffic leading to wrecks and species introductions, pressure to increase fishing effort beyond sustainable levels and the impacts of climate change all could potentially increase in the coming years. The United Kingdom has committed to protection of marine environments across the UKOTs, including Tristan da Cunha and these results can be used to inform future management decisions as well as provide a baseline against which future monitoring can be based.
Author: Caselle, Hamilton, Davis, Thompson, Turchik, Jenkinson, Simpson, Sala

Title: Recovery trajectories of kelp forest animals are rapid yet spatially variable across a network of temperate marine protected areas
Description: Oceans currently face a variety of threats, requiring ecosystem-based approaches to management such as networks of marine protected areas (MPAs). We evaluated changes in fish biomass on temperate rocky reefs over the decade following implementation of a network of MPAs in the northern Channel Islands, California. We found that the biomass of targeted (i.e. fished) species has increased consistently inside all MPAs in the network, with an effect of geography on the strength of the response. More interesting, biomass of targeted fish species also increased outside MPAs, although only 27% as rapidly as in the protected areas, indicating that redistribution of fishing effort has not severely affected unprotected populations. Whether the increase outside of MPAs is due to changes in fishing pressure, fisheries management actions, adult spillover, favorable environmental conditions, or a combination of all four remains unknown. We evaluated methods of controlling for biogeographic or environmental variation across networks of protected areas and found similar performance of models incorporating empirical sea surface temperature versus a simple geographic blocking term based on assemblage structure. The patterns observed are promising indicators of the success of this network, but more work is needed to understand how ecological and physical contexts affect MPA performance. © 2015, Nature Publishing Group. All rights reserved., Export Date: 2 October 2015
Author: Caselle, Rassweiler, Hamilton, Warner
Date: 2015-01-01T00:00:00Z

Title: Geographic variation in natal and early larval trace-elemental signatures in the statoliths of the market squid Doryteuthis (formerly Loligo) opalescens,
Description: , , , We found distinct geographic differences in trace element concentrations in both the core and early larval areas of the statoliths of paralarval market squid Doryteuthis (= Loligo) opalescens at sites throughout the Southern California Bight, USA. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) of individual statoliths indicated detectable levels of Mg, Mn, Sr, and Ba, with marginal levels of Cr and Pb. While these paralarvae showed considerable within-sample differences in elemental concentrations, there was significant between-site discrimination of natal (core) and early larval signatures for collection sites up to 100 km apart. In 2002 and 2003, levels of Ba and Sr in the statolith cores were significantly different among sites, suggesting differences in the natal environment or local maternal effects. Site specific differences in elemental signatures were also apparent for Mg and Mn in samples taken from outside the core in the early post-hatching period. These same portions of the statolith can be analyzed from adult squid collected on spawning grounds. We showed that concentrations of trace elements in the statolith cores of adults closely resembled the core signatures of squid paralarvae, which opens the possibility of identifying the source populations for stocks of this commercially important species., ,
Author: Warner, Hamilton, Sheehy, Zeidberg, Brady, Caselle
Date: 2009-01-01T00:00:00Z

Title: The interaction of retention, recruitment, and density-dependent mortality in the spatial placement of marine reserves,
Description: Population density can affect rates of mortality and individual growth. We measured these for the nonexploited bluehead wrasse, Thalassoma bifasciatum, at three sites around St. Croix, US Virgin Islands. Previous work demonstrated that differences in the degree of larval retention in these sites results in very large differences in recruitment intensity. Post-settlement mortality differed among sites and was positively related to recruitment density. Post-settlement growth differences were small. Because of strong mortality effects early in life, adult densities and size/age distributions differed among sites and did not reflect differences in recruitment rate. The site with the highest retention and recruitment (Butler Bay) had many small fish, while the two other sites with lower recruitment rates (Jacks Bay and Green Cay) had proportionally more large fish. These differences resulted in large differences in egg production. Per capita production was highest at the lowest density site (Green Cay). Total egg production at Green Cay was 75% that at Butler Bay, despite only having half the population size, and the highest overall production was at Jacks Bay, with low retention and moderate recruitment. In terms of marine reserve location, sites predicted to have high retention and recruitment may not always be the sites of highest egg production due to density-dependent processes, and it is important to consider the relative values of self-recruitment and larval export in reserve design., , ,
Author: Caselle, Hamilton, Warner
Date: 2003-01-01T00:00:00Z

Title: Utilizing spatial demographic and life history variation to optimize sustainable yield of a temperate sex-changing fish
Description: Fish populations vary geographically in demography and life history due to environmental and ecological processes and in response to exploitation. However, population dynamic models and stock assessments, used to manage fisheries, rarely explicitly incorporate spatial variation to inform management decisions. Here, we describe extensive geographic variation in several demographic and life history characteristics (e.g., size structure, growth, survivorship, maturation, and sex change) of California sheephead (Semicossyphus pulcher), a temperate rocky reef fish targeted by recreational and commercial fisheries. Fish were sampled from nine locations throughout southern California in 2007-2008. We developed a dynamic size and age-structured model, parameterized separately for each location, to assess the potential cost or benefit in terms of fisheries yield and conservation objectives of changing minimum size limits and/or fishing mortality rates (compared to the status quo). Results indicate that managing populations individually, with location-specific regulations, could increase yield by over 26% while maintaining conservative levels of spawning biomass. While this local management approach would be challenging to implement in practice, we found statistically similar increases in yield could be achieved by dividing southern California into two separate management regions, reflecting geographic similarities in demography. To maximize yield, size limits should be increased by 90 mm in the northern region and held at current levels in the south. We also found that managing the fishery as one single stock (the status quo), but with a size limit 50 mm greater than the current regulations, could increase overall fishery yield by 15%. Increases in size limits are predicted to enhance fishery yield and may also have important ecological consequences for the predatory role of sheephead in kelp forests. This framework for incorporating demographic variation into fisheries models can be exported generally to other species and may aid in identifying the appropriate spatial scales for fisheries management. © 2011 Hamilton et al., Cited By (since 1996):3, Fish and Fisheries, Art. No.: e24580
Author: Hamilton, Wilson, Ben-Horin, Caselle
Date: 2011-01-01T00:00:00Z

Title: Exploitation and recovery of a sea urchin predator has implications for the resilience of southern California kelp forests
Description: Size-structured predator–prey interactions can be altered by the history of exploitation, if that exploitation is itself size-selective. For example, selective harvesting of larger sized predators can release prey populations in cases where only large individuals are capable of consuming a particular prey species. In this study, we examined how the history of exploitation and recovery (inside marine reserves and due to fisheries management) of California sheephead (Semicossyphus pulcher) has affected size-structured interactions with sea urchin prey in southern California. We show that fishing changes size structure by reducing sizes and alters life histories of sheephead, while management measures that lessen or remove fishing impacts (e.g. marine reserves, effort restrictions) reverse these effects and result in increases in density, size and biomass. We show that predation on sea urchins is size-dependent, such that the diet of larger sheephead is composed of more and larger sized urchins than the diet of smaller fish. These results have implications for kelp forest resilience, because urchins can overgraze kelp in the absence of top-down control. From surveys in a network of marine reserves, we report negative relationships between the abundance of sheephead and urchins and the abundance of urchins and fleshy macroalgae (including giant kelp), indicating the potential for cascading indirect positive effects of top predators on the abundance of primary producers. Management measures such as increased minimum size limits and marine reserves may serve to restore historical trophic roles of key predators and thereby enhance the resilience of marine ecosystems.
Author: Hamilton, Caselle
Date: 2015-01-01T00:00:00Z

Title: Reassessment of the fecundity of California sheephead,
Description: Fecundity estimates used in a 2004 stock assessment to evaluate the overall health of the population of California sheephead Semicossyphus pulcher were based primarily on two studies. The first estimated the total fecundity of only nine individuals captured near Santa Catalina Island, California, and the second estimated batch fecundity of individuals taken from only one artificial reef. In order to develop a current and more comprehensive estimate of fecundity, we collected California sheephead from seven locations off southern California throughout the spawning season (July through September). To estimate both total fecundity and batch fecundity, we categorized and counted oocytes from ovarian subsamples of 28 and 24 (respectively) mature females (stage 3, spawning capable; determined by histological analysis). Total and batch fecundity increased with somatic mass, standard length, and ovary mass. We found total fecundity to increase with somatic mass to a power of 5.5, which is considerably greater than the value (2.95) reported previously. Our observations therefore highlight the importance of large females in the reproductive potential of the California sheephead stock. Regression analysis indicates that ovary mass is the most accurate biological indicator of fecundity for California sheephead and should be used for subsequent stock analyses., , ,
Author: Loke-Smith, Floyd, Lowe, Hamilton, Caselle, Young
Date: 2012-01-01T00:00:00Z

Title: Extensive geographic and ontogenetic variation characterizes the trophic ecology of a temperate reef fish on southern California (USA) rocky reefs,
Description: Interactions between predator and prey act to shape the structure of ecological communities, and these interactions can differ across space. California sheephead Semicossyphus pulcher are common predators of benthic invertebrates in kelp beds and rocky reefs in southern California, USA. Through gut content and stable isotope (δ 13C and δ 15N) analyses, we investigated geographic and ontogenetic variation in trophic ecology across 9 populations located at island and mainland sites throughout southern California. We found extensive geographic variation in California sheephead diet composition over small spatial scales. Populations differed in the proportion of sessile filter/suspension feeders or mobile invertebrates in the diet. Spatial variation in diet was highly correlated with other life history and demographic traits (e.g. growth, survivorship, reproductive condition, and energy storage), in addition to proxies of prey availability from community surveys. Multivariate descriptions of the diet from gut contents roughly agreed with the spatial groupings of sites based on stable isotope analysis of both California sheephead and their prey. Ontogenetic changes in diet occurred consistently across populations, despite spatial differences in size structure. As California sheephead increase in size, diets shift from small filter feeders, like bivalves, to larger mobile invertebrates, such as sea urchins. Our results indicate that locations with large California sheephead present, such as many marine reserves, may experience increased predation pressure on sea urchins, which could ultimately affect kelp persistence. © Inter-Research 2011., Cited By (since 1996):6, CODEN: MESED, ,
Author: Hamilton, Caselle, Lantz, Egloff, Kondo, Newsome, Loke-Smith, Pondella II, Young, Lowe
Date: 2011-01-01T00:00:00Z

Title: Consistent long-term spatial gradients in replenishment for an island population of a coral reef fish
Description: The population replenishment of marine organisms is routinely characterized as highly variable and unpredictable in space and time. Using island-wide recruitment surveys of a common coral reef fish, the bluehead wrasse Thalassoma bifasciatum, in 6 summers spanning a 12 yr period (1991 to 2003), we examined whether spatial patterns of recruitment are consistent or variable through time on St. Croix, US Virgin Islands. Despite annual fluctuations in the magnitude of replenishment, recruitment intensity follows a distinct and consistent spatial gradient that differs in direction between the north (leeward) and south (windward) shores; recruitment declines from west to east on the north shore and east to west on the south shore. The rank ordering of sites on each shore was concordant when recruitment was either pooled across years (monthly variation) or pooled across months (annual variation). When the 2 highest recruitment sites on each shore were considered alone, consistent seasonal effects were also apparent, with higher recruitment from June through August on the north shore, and higher recruitment in September on the south shore. Thus, while the magnitude of recruitment is indeed variable in space and time, its qualitative pattern is predictable in this area. Results of prior investigations of larval dispersal and coastal oceanography around St. Croix shed light on the origin of the consistent recruitment patterns documented in this study. The potential for consistent spatial and temporal patterns in recruitment is an important consideration in the spatial management of marine resources.
Author: Hamilton, White, Caselle, Swearer, Warner

Title: Incorporating biogeography into evaluations of the Channel Islands marine reserve network,
Description: , , , Networks of marine reserves are increasingly a major component of many ecosystem-based management plans designed to conserve biodiversity, protect the structure and function of ecosystems, and rebuild and sustain fisheries. There is a growing need for scientific guidance in the design of network-wide monitoring programs to evaluate the efficacy of reserves at meeting their conservation and management goals. Here, we present an evaluation of the Channel Islands reserve network, whichwas established in 2003 off the coast of southern California. This reserve network spans a major environmental and biogeographic gradient, making it a challenge to assess network-wide responses of many species. Using fish community structure data from a long-term, large-scale monitoring program, we first identified persistent geographic patterns of community structure and the scale at which sites should be grouped for analysis. Fish communities differedmost among islandswith densities of individual species varying from 3- to 250-fold. Habitat structure differed among islands but not based on reserve status. Across the network, we found that, after 5 years, species targeted by fishing had higher densities (1.5×) and biomass (1.8×) inside reserves, whereas nontargeted species showed no significant differences. Examining trophic groups, piscivore and carnivore biomass was significantly greater inside reserves (1.8× and 1.3× more, respectively), whereas the biomass of planktivores and herbivores was similar inside and out. A framework for incorporating biogeographic variation into reserve network assessments is critical as we move from the evaluation of single reserves to networks of reserves., ,
Author: Hamilton, Caselle, Malone, Carr
Date: 2010-01-01T00:00:00Z

Title: Ecosystem assessment of the Tristan Da Cunha Islands
Description: In January–February 2017, National Geographic’s Pristine Seas project, in collaboration with the Royal Society for the Protection of Birds (RSPB) and the Tristan da Cunha Government (including the Fisheries and Conservation Departments) conducted a 21-day expedition to Tristan da Cunha, Nightingale, Inaccessible and Gough Islands. The primary goals of the expedition were to conduct comprehensive quantitative surveys of the health of the archipelago’s largely unknown marine environment to assist the Government and people of Tristan da Cunha in planning marine protection . The results of the expedition highlight the unique marine ecosystem of this archipelago, particularly the pelagic and deep-sea environments, which were virtually unstudied and documented scientifically.The work presented in this report is meant to complement ongoing research at Tristan da Cunha and provide a springboard to help inform the Tristan Government about potential protection schemes that protect both important fisheries and unique biodiversity of the archipelago. .
Author: Caselle, Hamilton, Davis, Bester, Wege, Thompson, Turchik, Jenkinson, Simpson, Mayorga