Behavioral Immunity Suppresses an Epizootic in Caribbean Spiny Lobsters

Sociality has evolved in a wide range of animal taxa but infectious diseases spread rapidly in populations of aggregated individuals, potentially negating the advantages of their social interactions. To disengage from the coevolutionary struggle with pathogens, some hosts have evolved various forms of “behavioral immunity”; yet, the effectiveness of such behaviors in controlling epizootics in the wild is untested. Here we show how one form of behavioral immunity (i.e., the aversion of diseased conspecifics) practiced by Caribbean spiny lobsters (Panulirus argus) when subject to the socially transmitted PaV1 virus, appears to have prevented an epizootic over a large seascape. We capitalized on a "natural experiment" in which a die-off of sponges in the Florida Keys (USA) resulted in a loss of shelters for juvenile lobsters over a ~2500km² region. Lobsters were thus concentrated in the few remaining shelters, presumably increasing their exposure to the contagious virus. Despite this spatial reorganization of the population, viral prevalence in lobsters remained unchanged after the sponge die-off and for years thereafter. A field experiment in which we introduced either a healthy or PaV1-infected lobster into lobster aggregations in natural dens confirmed that spiny lobsters practice behavioral immunity. Healthy lobsters vacated dens occupied by PaV1-infected lobsters despite the scarcity of alternative shelters and the higher risk of predation they faced when searching for a new den. Simulations from a spatially-explicit, individual-based model confirmed our empirical results, demonstrating the efficacy of behavioral immunity in preventing epizootics in this system.     

Temperature acclimation alters cardiac performance in the lobster Homarus americanus

The American lobster is a poikilotherm that inhabits a marine environment where temperature varies over a 25°C range and depends on the winds, the tides and the seasons. To determine how cardiac performance depends on the water temperature to which the lobsters are acclimated we measured lobster heart rates in vivo. The upper limit for cardiac function in lobsters acclimated to 20°C is approximately 29°C, 5°C warmer than that measured in lobsters acclimated to 4°C. Warm acclimation also slows the lobster heart rate within the temperature range from 4 to 12°C. Both effects are apparent after relatively short periods of warm acclimation (3–14 days). However, warm acclimation impairs cardiac function at cold temperatures: following several hours exposure to frigid (<5°C) temperatures heart rates become slow and arrhythmic in warm acclimated, but not cold acclimated, lobsters. Thus, acclimation temperature determines the thermal limits for cardiac function at both extremes of the 25°C temperature range lobsters inhabit in the wild. These observations suggest that regulation of cardiac thermal tolerance by the prevailing environmental temperature protects against the possibility of cardiac failure due to thermal stress.     

Ecological and physiological effects of PaV1 infection on the Caribbean spiny lobster (Panulirus argus Latreille)

Pathogens can profoundly impact the ecology of the organisms they infect through changes in host behavior that influence demographic processes. For example, juvenile Caribbean spiny lobsters (Panulirus argus Latreille) infected with the PaV1 virus (Panulirus argus Virus 1) are avoided by their normally social conspecifics, which alters local spatial distributions and presumably rates of disease transmission. PaV1 infections are nearly always lethal, but prior to succumbing to the disease, infection may impact other host dynamics (e.g., movement, growth, or survival) that effect transmission of the virus. We used mark-recapture surveys and laboratory studies to determine the impact of PaV1 infection on lobster movement and physiological condition, and in turn, the effect of condition on susceptibility to infection. Significantly more healthy lobsters were recaptured than heavily diseased lobsters in 5-d mark-recapture surveys, indicating either greater emigration or greater mortality of infected lobsters. Results of a laboratory bioassay suggest that lobsters with early-stage infections moved at an equivalent rate to healthy lobsters, however, as infection progressed, lobsters inoculated with PaV1 moved less than healthy lobsters ultimately remaining sedentary. Infected lobsters captured in nature also had significantly lower hemolymph (blood) serum protein values, indicating poor physiological condition. However, poor condition did not predispose lobsters to greater risk of infection because prevalence was not different between starved lobsters and healthy lobsters challenged with PaV1. Although lobsters infected with PaV1 eventually become sedentary and of poor nutritional condition, during the early stages of infection they remain active and are thus capable of dispersing the virus throughout the population.     

Daily and circadian rhythms of locomotor activity in the American lobster, Homarus americanus

It is widely accepted that American lobsters, Homarus americanus (Milne-Edwards), are nocturnally active. However, the degree to which this rhythm is expressed by different individuals and the underlying causes of lobster activity rhythms, are poorly understood. In order to address these issues we recorded daily patterns of lobster locomotion using two novel techniques. In the first, reed switch assemblies were used to monitor the distance traveled by freely moving lobsters (n=43), each fitted with a small magnet, as they walked around a 1 m diameter racetrack. The advantages of this technique included: (1) lobsters were freely moving; (2) the system could be deployed in laboratory tanks or in the field and; (3) actual distances moved were measured, not just relative activity. The second technique involved placing individual lobsters (n=10) into custom-designed running wheels. This allowed for continuous monitoring of locomotor activity for extended durations (>45 days) under normal light/dark (L/D) cycles, as well as in constant darkness (D/D) and constant light (L/L).Under ambient light conditions lobsters in the racetracks moved an average of 60.1±6.5 m/day in flow-through seawater tanks. Overall, lobsters were significantly more active at night, moving 4.1±0.4 m/h in the dark vs. 1.0±0.2 m/h in the light. However, many of the lobsters moved as much during the day as during the night.Lobsters in the running wheels moved an average of 36.6±11.7 m/day and 80% expressed clear daily rhythms of activity, with a mean periodicity of 24.0±0.1 h under L/D conditions. Under D/D conditions 90% of the animals expressed free-running circadian rhythms with a mean periodicity of 24.2±0.3 h, indicating that this species possesses endogenous rhythmicity. While the running wheel results show that the nocturnal pattern of locomotor activity for this species is strongly influenced by an endogenous circadian clock, the results from the racetracks show that there is remarkable variability in the extent to which they express this pattern under natural conditions.     

Foraging patterns of juvenile western rock lobsters Panulirus cygnus George

Foraging patterns of juvenile western rock lobster Panulirus cygnus George were investigated in the field by tracking lobsters with electromagnetic tags for up to 3 wk. Most foraging activity begins in response to changes in light levels associated with dusk and not by diurnal changes in water temperature or currents. Similarly, lobsters return from foraging around dawn when light levels start to increase. Foraging activity was constant throughout the night, and males were more active than females. Lobsters usually moved at a rate of ≈ l m · min ⁻¹ at night, although sometimes they travelled up to 18m· min⁻¹ when walking over bare sand. They often lived on one reef but travelled to forage on seagrass beds in front of another reef, sometimes visiting a den on that reef. Some lobsters used several dens on different reefs during the 3 wk of observation. Although lobsters foraged in both of the two main structural varieties of seagrass beds, Amphibolis and Heterozostera with Halophila, they foraged for longer periods in the Heterozostera with Halophila beds. Foraging ranges varied within and between individuals although an individual lobster might forage in the same general area on a few successive nights or even up to several weeks.     

Overview,opportunities and outlook for Australian spiny lobster fisheries

Australia’s lobster fisheries are relatively small in volume (9500t) compared with global production (289,000t), but are the country’s most valuable in terms of both overall production and value of export (2014 Gross Value of Production of $610 million AUD). Further, they support commercial, recreational and indigenous fishers along most of the continent’s coastline. Here we review similarities and key differences between these lobster fisheries, based on biological characteristics, fishery data collection, assessment and management methods, and supply chain considerations. A diverse range of palinurid lobsters occur in Australia, but only three genera, distributed across eight different management jurisdictions, support significant fisheries. Catches of western rock lobster Panulirus cygnus dominate landings (61%), followed by southern rock lobster Jasus edwardsii, tropical lobster Panulirus ornatus and the eastern rock lobster Sagmariasus verreauxi. Large-scale environmental influences such as climate change are impacting on these fisheries in similar or different ways forcing new management and raising the need for greater resilience in current supply chains. Although these are separate fisheries, the integrated nature of the dominant Chinese export markets suggests potentially important economic and market-related interactions. Our overview highlights the critical role of continued monitoring of recruitment pulses, in combination with robust harvest strategies, to ensure that harvests respond adequately and fisheries achieve biological and economic sustainability. Approaches that also include socio-cultural considerations (triple bottom line) are important given many fisheries include indigenous Australians. Our integrated analysis of Australian lobster fisheries highlights differences and similarities with spiny lobster fisheries worldwide and lessons from opportunities, including adapting to new free trade agreements, enhancing the reputation of wild lobsters as a whole, sharing expertise, and better alignment of supply and demand.     

Restricted movement of the fluvial form of red-spotted masu salmon,Oncorhynchus masou rhodurus,in a mountain stream,Central Japan

Movement of the fluvial form of red-spotted masu salmon (1⁺ and older),Oncorhynchus masou rhodurus, was studied using mark-recapture methods in a Japanese mountain stream. Most (63–91%) adult salmon were recaptured in the pool in which they were marked. The rest of the salmon moved upstream or downstream <20m during the non-breeding period. The proportion of the salmon moving increased slightly during the breeding period, but did not exceed 66%. The distance moved was also more variable during this period. The proportion of the smaller salmon which moved was larger than that of the larger fish during the non-breeding period. Conversely, during the breeding period, larger fish moved more frequently. Sedentary behaviour and local movements of adult salmon seem to be affected by their social relationships.     

Historical translocations and stocking alter the genetic structure of a Mediterranean lobster fishery

Stocking is often used to supplement wild populations that are overexploited or have collapsed, yet it is unclear how this affects the genetic diversity of marine invertebrate populations. During the 1970s, a lobster stock enhancement program was carried out around the island of Corsica in the Mediterranean using individuals translocated from the Atlantic coast of France. This included the release of thousands of hatchery‐reared postlarval lobsters and several adult individuals, but no monitoring plan was established to assess whether these animals survived and recruited to the population. In this study, we sampled European lobster (Homarus gammarus) individuals caught around Corsica and tested whether they showed Atlantic ancestry. Due to a natural marked phylogeographic break between Atlantic and Mediterranean lobsters, we hypothesized that lobsters with dominant (>0.50) Atlantic ancestry were descended from historical stocking releases. Twenty Corsican lobsters were genotyped at 79 single nucleotide polymorphisms, and assignment analysis showed that the majority (13) had dominant Atlantic ancestry. This suggests that the hatchery stocking program carried out in Corsica during the 1970s, using individuals translocated from the Atlantic coast of France, has likely augmented local recruitment but at a cost of altering the genetic structure of the Corsican lobster population.     

Ontogenetic shifts in resource allocation: colour change and allometric growth of defensive and reproductive structures in the Caribbean spiny lobster Panulirus argus

Resource allocation theory predicts a disproportionately large allocation of resources to defensive structures during early ontogeny in organisms that are subject to more intense predation at smaller than at larger body sizes. We tested this prediction on the Caribbean spiny lobster Panulirus argus, which exhibits a negative relationship between predation risk and body size with a high natural mortality of smaller individuals. Independent allometric growth analyses demonstrated that numerous defensive structures (e.g. orbital horns, segments supporting the antenna, the tail fan) display negative allometric growth throughout ontogeny. We interpret these findings as lobsters investing disproportionately more resources to defensive structures when small to improve survivorship. Similarly, we observed an ontogenetic shift in lobster colour pattern; small individuals (< 23 mm carapace length) that inhabit nursery grounds (preferably among red algae) displayed a disruptive pattern (camouflage), whereas larger juveniles displayed a bicolour pigmentation typical of adult lobsters. This shift in colour pattern further suggests that small lobsters employ cryptic coloration throughout their asocial algal stage. However, this cryptic coloration offers no advantage when lobsters grow larger and start dwelling in crevices. Other structures linked to reproduction (e.g. female pleopods and male pereopods) experienced either isometric or positive allometric growth throughout ontogeny. Our results support one of the main predictions of resource allocation theory and demonstrate ontogenetic shifts in defensive structures and coloration concomitantly with changes in lobster mortality risk mediated by size‐dependent predation risk. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Comparison of injuries to New Zealand rock lobsters (Jasus edwardsii) caused by hand versus snare collection

Abstract

Following the prohibition in New Zealand of lobster snares in late 2005, we undertook research to compare the frequency and extent of injuries to rock lobsters (Jasus edwardsii) (Hutton) caused by recreational SCUBA divers using lobster snares compared with hand collection. Rock lobsters were sampled between January 2006 and October 2006 from multiple dive sites around the North Island of New Zealand. Of the 124 rock lobsters caught, 20.9% were in a soft shell state. Female rock lobsters constituted 43.5% of the catch, but only one was carrying eggs. Female mean tail width was 72.2 mm; male mean tail width was 71.9 mm. We found that hand collection caused significantly more injuries than snare collection, to both soft shell and hard shell animals. Hand collection also resulted in more major injuries, with 18% of hard shell animals and 31% of soft shell animals losing two or more limbs. We recommend that the prohibition on the use of rock lobster snares be lifted, as their use appears to significantly reduce injury and stress to rock lobsters in recreational dive areas, and increase the survival of undersized individuals released after capture.     

Home range,movements, and density of the central stoneroller,Campostoma anomalum,in a small Ohio stream

Synopsis A population of central stonerollers, Campostoma anomalum, in Harker's Run, Butler County, Ohio U.S.A., was examined during autumn, 1980, to determine the species' movements, density, and home range size. During the study period, 170 fish were marked by fin clips and released into the specific pool or riffle where they were captured within the 187 m study section. Eighty percent of the recaptured, marked fish (20) were recaptured in their initial capture area (specific pool or riffle). No fish moved more than 135 m from its original capture area. Density estimates of C. anomalum for each pool and riffle within the study section ranged from 0.10–3.91 fish m⁻² (mean = 1.25 fish m⁻²). Home range size was estimated to be 35.2 ± 14.1 m (mean ± 95% CI) of stream length. Campostoma anomalum in Harker's Run occurred at densities similar to those reported for the species in other streams, and their home ranges in this system were of similar size to those of other small, stream-dwelling fishes.     

Predation of the sea urchin Heliocidaris erythrogramma by rock lobsters (Jasus edwardsii) in no-take marine reserves

The formation of sea urchin ‘barrens’ on shallow temperate rocky reefs is well documented. However there has been much conjecture about the underlying mechanisms leading to sea urchin barrens, and relatively little experimentation to test these ideas critically. We conducted a series of manipulative experiments to determine whether predation mortality is an important mechanism structuring populations of the sea urchin Heliocidaris erythrogramma in Tasmania. Tethered juvenile and adult sea urchins experienced much higher rates of mortality inside no-take marine reserves where sea urchin predators were abundant compared to adjacent fished areas where predators were fewer. Mortality of tagged (but not tethered) sea urchins was also notably higher in marine reserves than in adjacent areas open to fishing. When a range of sizes of sea urchins was exposed to three sizes of rock lobsters in a caging experiment, juvenile sea urchins were eaten more frequently than larger sea urchins by all sizes of rock lobster, but only the largest rock lobsters (> 120 mm CL) were able to consume large adult sea urchins. Tagging (but not tethering) juvenile and adult sea urchins in two separate marine reserves indicated that adult sea urchins experience higher predation mortality than juveniles, probably because juveniles can shelter in cryptic microhabitat more effectively. In a field experiment in which exposure of sea urchins to rock lobster (Jasus edwardsii) and demersal reef fish predators was manipulated, rock lobsters were shown to be more important than fish as predators of adult sea urchins in a marine reserve. We conclude that predators, and particularly rock lobsters, exert significant predation mortality on H. erythrogramma in Tasmanian marine reserves, and that adult sea urchins are more vulnerable than smaller cryptic individuals. Fishing of rock lobsters is likely to reduce an important component of mortality in H. erythrogramma populations.     

Distribution and movement of domestic rainbow trout, <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>, during pulsed flows in the South Fork American River,California

We tracked the movements of ten small (SL = 25.5–31.0 cm) and ten large (SL = 32.0–38.5 cm) radio-tagged domestic rainbow trout (Oncorhynchus mykiss) in response to frequent pulsed releases of water in the South Fork American River (California) from July to October 2005. In week one all the small trout moved less than 1 km upstream or downstream of their release sites. Four small trout moved 1–3 km upstream or downstream of their release sites in the following 8 weeks. Seven out of ten large trout moved downstream after their release. In subsequent weeks most large trout showed smaller upstream and downstream movements, and were observed between 1 km upstream and 8 km downstream of their release sites. Our results suggest that domestic rainbow trout with SL > 25 cm are not forced downstream by daily pulsed flow increases from 5 to over 40 m³s⁻¹.     

Spatial overlap and interaction between sub-adult American lobsters, Homarus americanus, and the invasive European green crab Carcinus maenas

Invasive species are considered one of the major threats to biological diversity, and they can negatively impact species of particular ecological and/or economic importance. In this study, we investigate the potential threat that the European green crab, Carcinus maenas, represents to sub-adult lobsters, Homarus americanus, in Passamaquoddy Bay, Canada, northwest Atlantic. We conducted transect surveys using SCUBA diving to evaluate spatial overlap between these species inside, and immediately adjacent to, a lobster nursery area, and ran two laboratory experiments to investigate interactions between them in conditions of limited food and shelter availability. We found marked spatial overlap between these species in nature, particularly between adult green crabs and sub-adult lobsters in the shallower parts of the nursery area. It was not uncommon to see green crabs and sub-adult lobsters less than 1-2 m from one another, and we estimated mean nearest-neighbor values as low as 0.5-1 m on certain transects and months, with a grand mean of 5.17 ± 1.62 m (SE). Monte Carlo randomization of positional data revealed that green crabs and lobsters were randomly distributed relative to one another; individuals of one species did not seem to aggregate or segregate relative to individuals of the other species. In the lab, green crabs did not negatively affect survival (one exception), growth, activity, feeding, or shelter use of sub-adult lobsters. In fact, sub-adult lobsters regularly preyed upon green crabs in the first lab experiment, where heterospecific individuals were matched for body mass. Our results suggest that green crabs do not pose a significant threat to sub-adult lobsters in Passamaquoddy Bay, and may in fact represent a food subsidy for them.     

Identification of steroid hormones and fatty acids during gonadal maturation of spiny lobster Panulirus homarus

Information on steroid hormones and fatty acids that play roles in lobster reproduction is still very limited although the data are indispensable to seed production in hatchery. The study was designed to identify steroid hormones and fatty acids during gonadal maturation of spiny lobster (Panulirus homarus). Male spiny lobsters were treated with and without thyroxine injection. Female spiny lobsters were treated with and without eyestalk ablations during mature and immature gonad developments. Androst-5-en-17-one,3β (androst) and estran-3-one,17β (estran), two steroid hormones were identified at different levels of gonadal maturity of spiny lobsters. High concentrations of androst and estran were detected in the male spiny lobsters treated with thyroxine injections. Estran showed high concentrations in female brood stock of spiny lobsters during oogenesis stages both without eyestalk ablation and with ablation of one or two eyestalks, except in the immature female gonads. It was found that stearic acid was the highest and dominant fatty acid in mature male spiny lobster. Stearic acid, oleic acid, palmitic acid and caprylic acid were fatty acids with high concentrations in immature and mature female spiny lobsters. After 30 days in captivity, only stearic acid and oleic acid were found dominantly in eyestalk ablated mature female spiny lobsters.     

Breeding site fidelity in penduline tit Remiz pendulinus in Southern Hungary

Birds move between breeding locations to gain a better territory, avoid competition or reduce the deleterious effect of inbreeding. We investigated breeding site fidelity in a small European passerine, the penduline tit (Remiz pendulinus). This species has an exceptionally diverse breeding system, in which both males and females may have up to 5–7 mates in a single breeding season, and the eggs are incubated by a single parent: either the male or the female. We investigated the movements of males and females within three breeding seasons in Southern Hungary (2002–2004). Males moved for shorter distances between breeding sites (116 m, 63–333 m; median, lower quartile–upper quartile) than females (942 m, 415–2,382 m). Movements of males and females were consistent between years, and they were repeatable between subsequent nests of males, but not of females. Taken together, our results suggest that adult male penduline tits are more site-faithful than adult females. We suggest that this difference has an implication on their breeding ecology since male parental behaviour (desert/care) is expected to be influenced by local mating opportunities, whilst female parental behaviour is likely to depend on the mating opportunities in a large area around their breeding site.     

Natal dispersal of introduced Siberian chipmunks, <Emphasis Type="Italic">Tamias sibiricus</Emphasis>, in a suburban forest

The Siberian chipmunk, Tamias sibiricus, was introduced into the suburban forest of Sénart in the late 1970s where it naturalised. Juvenile dispersal of this solitary ground-dwelling squirrel is not known, while it is an important component of the invasion process. From 2003 to 2007, mark–recapture techniques were used to determine how dispersal movements differed between year, cohort, sex and body mass. Distances moved were calculated between the location of first capture during the year of birth and the arithmetic centre of the trapping locations obtained the next year. Excluding heaviest individuals, e.g. 80 g, that must have already dispersed and thus lowered the estimation of averaged distance moved, our results shows that the dispersal distance in juvenile males (168 ± 24 m, n = 39) was greater than in females (83 ± 11 m, n = 66), with no effect detected for either year or cohort. Juveniles are thus involved in the spread of this ground squirrel, bearing in mind that movements estimated may have been underestimated due to the use of capture–mark–recapture methods on a limited trapping area.     

Movements and Site Fidelity of two Juvenile Fish Species Using Surf Zone Nursery Habitats Along The Southeastern North Carolina Coast

We examined the extent of movements of juvenile Florida pompano, Trachinotus carolinus, and gulf kingfish, Menticirrhus littoralis, along an open ocean beach. Fishes were collected by seine at three sites along Masonboro Island and Carolina Beach, NC between 7 June and 7 July 1995. All specimens 40 mm standard length (SL) were tagged with coded wire tags and released at the capture sites. Between 7 July and 9 August and on 15–16 September Masonboro Island and northern Carolina Beach were surveyed for tagged fish. A controlled tag mortality/retention study was conducted for both species. Overall, 1569 Florida pompano (40–135 mm SL) were tagged. Sixty-one (3.9%) of these were recaptured, and only eight moved away from the original tagging sites. The largest movements by two Florida pompano were 2.1 and 10.5 km. Many fish remained at their original tagging sites for 21–27 days. Of 488 gulf kingfish (36–158 mm SL) tagged, 16 (3.3%) were recaptured. Gulf kingfish also exhibited little movement away from tagging sites during the study, with individuals remaining at original tagging sites up to 21 days. Stock size estimates for Florida pompano ranged from 3354 to 4670 among the tagging sites, with densities ranging from 1.9 to 2.6 fish m^–2. The remarkable site fidelity exhibited by these two species suggests that resources were not limiting or that predation pressure was not high enough to cause large scale movements during the study. This implies that local disturbances could impact behavior or survival of juvenile fishes in the surf zone.     

Enhancement of juvenile Caribbean spiny lobsters: an evaluation of changes in multiple response variables with the addition of large artificial shelters

Shortage of natural crevice shelters may produce population bottlenecks in juvenile Caribbean spiny lobsters (Panulirus argus), a socially gregarious species. We conducted a field experiment to test enhancement of a local population of juvenile P. argus with the addition of artificial shelters (“casitas”) that mimic large crevices (1.1 m² in surface area and 3.8 cm in height). Changes in density and biomass of juvenile lobsters 15–50 mm carapace length (CL) were assessed with a multiple before-after control-impact (MBACI) analysis. Separate analyses were also conducted on small (15–35 mm CL) and large (35.1–50 mm CL) juveniles to assess size-related effects. First, we carried out 13 lobster surveys on nine fixed 1-ha sites over a shallow reef lagoon (“before” period). Then, we deployed ten casitas in each of five sites and left four sites as controls, and conducted 22 further surveys (“after” period). Deployment of casitas resulted in a sixfold increase in juvenile density (76% contributed by small and 24% by large juveniles) and a sevenfold increase in biomass (40 and 60%, respectively). Capture–recapture results revealed that enhancement was achieved not by promoting individual growth but by increasing survival, persistence, and foraging ranges of small and large juveniles. Casitas both mitigated shortage of natural shelter and increased sociality, allowing for cohabitation of smaller, more vulnerable juveniles with larger conspecifics that have greater defensive abilities. Casitas may help enhance local populations of juvenile P. argus in Caribbean seagrass habitats, typically poor in natural crevice shelters. The use of MBACI and the simultaneous assessment of multiple interrelated response variables may be a powerful analytical approach to test shelter limitation in other species and to examine the function of structural habitat in other systems.     

Migration of green sturgeon, Acipenser medirostris, in the Sacramento River

Adult green sturgeon, Acipenser medirostris, were collected in San Pablo Bay, California, and surgically implanted with ultrasonic acoustic tags from 2004 to 2006. An array of automated acoustic monitors was maintained in the Sacramento River to record movements of these fish. We presumed movements to known spawning areas (based on previous green sturgeon egg collections) or areas with potential spawning habitat (characterized by substrate, flow, and temperature criteria) represented a “spawning migration.” Three separate annual “spawning migrations” were recorded involving 15 individuals. The majority of the Sacramento River migrants entered the system in the months of March and April. Two different patterns of “spawning migration” and out-migration were observed. Six individuals potentially spawned, over-summered and moved out of the river with the first fall flow event. This is believed to be the common behavior of the green sturgeon. Alternatively, nine individuals promptly moved out of the Sacramento River before 1 September, and any known flow or temperature cue. Some green sturgeon appeared to be impeded on their upstream movement by the 15 May closure of the Red Bluff Diversion Dam, and at least five passed under the dam gates during downstream migration. A delay in the closure of the Red Bluff Diversion Dam would likely allow upstream passage of spawning green sturgeon, further, the potential mortality affects of downstream passage beneath the Red Bluff Diversion Dam should be assessed. Specific protection should be also given to the large aggregation of green sturgeon located in the reach of the Sacramento River adjacent to the Glen Colusa Irrigation District pumping facility.