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... The Pacific geoduck Panopea generosa is an ideal study species to investigate geographic variation in life history and morphology because of its large geographic range. As an occupant of intertidal and subtidal soft substrates from Alaska to Baja California (Andersen 1971, Goodwin & Pease 1987, this clam is one of the largest burrowing bivalves in the world. Given its large size, commercial and recreational fisheries target P. generosa along the Pacific coast of North America, subjecting clam populations to the highest levels of exploitation (and selection pressures that may alter life history traits) at the northern and southern ends of the species range, in Washington and Baja California, Mexico, where commercial fisheries operate. ...
... Because geoducks typically live below mean lower low water, predators such as fishes may also feed on geoducks. Andersen (1971) observed that siphon damage caused by predatory fishes, such as the cabezon (Scorpaenichthys marmoratus) and the spiny dogfish (Squalus acanthias) could impact growth. Both fishes are known to frequent Bodega Bay and Morro Bay waters and occur commonly at the subtidal locations sampled. ...
... With an average larval duration of 47 days (Andersen 1971), there is a potential for high gene flow and extensive population connectivity across the species range of Panopea generosa, from Alaska to Baja California. Vadopalas et al. (2004) reported genetic patchiness of P. generosa populations using microsatellite markers, but their study did not include the entire range of P. generosa. ...
... Early tag and recapture studies to measure the growth rates of P. abrupta in Washington indicated that growth was rapid in small geoducks and minimal in older clams (e.g., Goodwin, 1973). However, in several studies the tagging process resulted in a suppression of growth rates and a high level of mortality with few tagged geoducks being recaptured (e.g., Andersen, 1971; Goodwin, 1973 Goodwin, , 1976). The poor recovery rate of P. zelandica from Shelly Bay (most likely a result of high mortality) and the lack of growth in those geoducks that were retrieved, further indicate that this is not a suitable method for assessing the growth rate of geoducks. ...
... hose geoducks that were retrieved, further indicate that this is not a suitable method for assessing the growth rate of geoducks. However, an ability to determine the size of geoducks from the width between paired siphon holes would be a useful tool for assessing the size structure of geoduck populations quickly without having to sacrifice animals. Andersen (1971) found no relationship between the width between paired siphons and the size of P. abrupta from Hood Canal, Washington . Our study found that the width between the siphons visible at the sediment surface was a reasonable predictor of the shell length (r 2 = 0.57) for P. zelandica in Kennedy Bay. However, there was a great deal of variati ...
... Given that the largest siphon holes are most easily found and generally contain the largest geoducks, there is the possibility that any fishery may inadvertently target large female geoducks resulting in populations that are egg-limited. Similar data sets with males dominating the smaller size classes and females becoming more prevalent as shell length increases have also been reported for P. abrupta (e.g., Andersen, 1971; Campbell and Ming, 2003). This may offer an alternative explanation to the fall in levels of recruitment observed in populations of P. abrupta. ...
There is increasing interest in developing fisheries and aquaculture industries for the New Zealand geoduck clam, Panopea zelandica (Quoy and Gaimard, 1835). However, little is known about the age structure, growth rates, and mortality of different populations of P. zelandica. Annual bands in polished shell sections were used to obtain estimates of age, growth rates, and mortality of P. zelandica at two sites in northern New Zealand. Panopea zelandica in Kennedy Bay ranged in age from 2 to 34 yrs whilst those in Shelly Bay ranged from 3 to 85 yrs. There was a significant difference (P < 0.001) in growth rates (shell length-at-age) between the populations (estimated asymptotes were 111.5 mm and 103.6 mm for Kennedy Bay and Shelly Bay, respectively). However, the growth characteristics (i.e., rapid growth for the first 1012 yrs and minimal thereafter) were similar for both populations. Drained wet weight-at-age followed a similar pattern to shell length-at-age, although growth in terms of weight was rapid until 1213 yrs of age. The estimated maximum drained wet weight of P. zelandica was higher in Kennedy Bay (275.5 g) than in Shelly Bay (223.1 g). There was also a significant difference (P = 0.02) in the relationship between total shell length and drained wet weight for the two populations. The width between the siphons visible at the sediment surface was a reasonable predictor of the shell length (r2=0.57) of P. zelandica in Kennedy Bay. Estimates of natural mortality using catch curve analysis, estimates of maximum age, and the Chapman-Robson estimator were very low (0.020.12 proportion yr-1). This study is the first to confirm that the shell bands in P. zelandica are deposited annually and can be successfully used to age this species. Given the low estimated rates of mortality and longevity of P. zelandica, fisheries managers will need to carefully consider the feasibility of commercially harvesting this species.
... The reproductive characteristics described by Campbell and Ming (2003) for P. abrupta and by Gribben et al. (2004) for P. zelandica coincide with those observed for P. globosa in the central Gulf of California (Noriega et al. 2007) and in the current study. In addition, the 3 cited species exhibit synchronous reproductive development and spawning (Andersen 1971, Gribben et al. 2004, Arago´nArago´n-Noriega et al. 2007). Because the environment and geographical regions where these species reside are completely different, this observation implies that the gametogenic cycle and timing of Panopea spp. ...
... P. globosa have a very short reproductive period of only 3 to 5 mo (Arago´nArago´n-Noriega et al. 2007, Arambula-Pujol et al. 2008) and an extended resting period during which clams could not be sexed. In contrast, P. zelandica have a resting phase of only 1–2 mo (Gribben et al. 2004), and reproduction of P. abrupta from Washington state and British Columbia is continuous with no resting period at all (Andersen 1971, Sloan & Robinson 1984). Gametogenic development for both P. abrupta and P. zelandica starts during late fall and winter when water temperatures are low; development continues and spawning occurs in spring and summer as water temperatures rise. ...
... This may indicate that this trait is genetically determined, and quite probably influenced by phylogenetic, conservative selective pressures. The divergence between the reproductive cycles of P. abrupta and P. zelandica, which spend ;10–12 mo in reproductive activity (Andersen 1971, Sloan & Robinson 1984, Gribben et al. 2004), and that of P. globosa, in which reproductive cells are present during only 4 or 5 mo and develop synchronously between sexes (Fig. 3 ; Noriega et al. 2007, ArambulaPujol et al. 2008), might well be explained by the conceptual planktonic larval development model of O'Connor et al. (2007). According to this model, the Cortes geoduck has been selected to start gametogenesis when conditions are still warm, and uses the seasonal drop in temperature as a trigger for gametogenesis. ...
This article describes the timing of gametogenic development and spawning in a population of geoduck clams, Panopea globosa (Dall 1898), from the Upper Gulf of California and its relationship to temperature changes and primary productivity. Clams were collected monthly over 1 year (March 2008 to March 2009), and salinity, dissolved oxygen, and substrate type were recorded during each survey. Standard histological analyses and measurements of oocyte diameters were used to describe the timing of gametogenic development and spawning. Satellite data for temperature and chlorophyll were gathered to test a general conceptual planktonic larval development model. The results demonstrated that reproductive activity was triggered by a steep decrease in temperature 4 months prior to the peak of productivity. Thus, larval development matches favorable conditions, as predicted by Cushing's Match—Mismatch Hypothesis.
... The reproductive characteristics of P. abrupta and P. zelandica are similar. They both show active gametogenesis during winter, are seasonal broadcast-spawners, the spawning season taking place from early spring to late summer, and spawning usually peaks during summer (Andersen, 1971; Goodwin, 1976; Sloan and Robinson, 1984; Breen et al., 1991; Gribben et al., 2004). In the case of P. abrupta, spawning is synchronous between sexes, although males show a less concise seasonal reproductive pattern than to females. ...
... Although sex ratios in clams rarely differ from 1:1 (Eversole, 1989), there is often a predominance of males at younger ages or smaller sizes (Gribben and Creese, 2003). The male to female ratio of mature P. abrupta and P. zelandica are similar, and the high percentages of males at small sizes (young ages) are also found in both species (Andersen, 1971; Campbell and Ming, 2003; Gribben and Creese, 2003). Gribben and Creese (2003) presented a validated ageing method which demonstrates that all immature clams develop first as males, with a certain proportion developing into females in subsequent years. ...
... Gribben and Creese (2003) presented a validated ageing method which demonstrates that all immature clams develop first as males, with a certain proportion developing into females in subsequent years. Moreover, in the North American geoduck, P. abrupta, males appear to mature at a smaller size than females, with the proportion of females increasing as size increase (Andersen, 1971; Campbell and Ming, 2003). The life span and maximum size of P. abbreviata are moderate compared to P. abrupta (Sloan and Robinson, 1984; Harbo et al., 1983), but similar to those reported for P. zelandica by Gribben and Creese (2003). ...
On the basis of histological examination, we present the first description of gametogenesis in Panopea abbreviata. Six stages of gonad development were identified using morphological and histochemical criteria. The gonads are diffuse and cannot be sexed with the naked eye. The analyses of gonad tissues showed that the gametogenic cycle is continuous with no resting period. Ripe individuals of both sexes were found for most of the year, and the spawning season seems to be protracted. The application of histological techniques to individuals collected monthly revealed a bias in the sex ratio depending on the body length. Even when the sex ratio was balanced in large clams, for small individuals, the sex ratio was biased in favour of the males. Although no hermaphroditic individuals were found in our samples, the possibility of protandry should be examined further.
... Geoduck clams exist in the southern and northern hemispheres over a broad geographical range and show latitudinal gradients in the timing of gametogenesis , spawning, and in the number of spawning events in a reproductive season (Gribben et al. 2004). Studies conducted on the northern geoduck Panopea generosa (0abrupta) (Andersen 1971; Goodwin 1976; Sloan & Robinson 1984; Campbell & Ming 2003) and on the southern geoduck P. zelandica (Breen et al. 1991; Gribben et al. 2004) show that both species exhibit synchronous reproductive development and spawning, having an annual reproductive cycle with a single spawning mode during warmer months. Specifically, gametogenesis of P. generosa starts in late summer and the early active and ripeness phases may extend, depending on the region, from SeptemberÁJanuary and from NovemberÁMay, respectively (Goodwin 1976; Turner & Cox 1981; Sloan & Robinson 1984; Feldman et al. 2004). ...
... Specifically, gametogenesis of P. generosa starts in late summer and the early active and ripeness phases may extend, depending on the region, from SeptemberÁJanuary and from NovemberÁMay, respectively (Goodwin 1976; Turner & Cox 1981; Sloan & Robinson 1984; Feldman et al. 2004). In Vancouver and the Gabriola Islands (Canada), spawning begins in middle to late May (Campbell & Ming 2003); in Washington and British Columbia it ranges from June through July (Andersen 1971; Sloan & Robinson 1984). Clams are spent by JulyÁAugust (Feldman et al. 2004). ...
The reproductive cycle of Panopea generosa at the southernmost limit of its distribution in the State of Baja California, Mexico was studied, using standard histological techniques, oocyte cohort analysis and a gonadosomatic index. The reproductive cycle of P. generosa begins in late autumn, with a developing phase in winter and continuous proliferation and spawning from April throughout October. During this period, several oocyte cohorts were developed, but only three attained maturity, the rest being reabsorbed into the gonad. Gamete reabsorption within the gonad might reflect a conservative pattern of nutrient recycling. Ripe gametes were continuously released with a main spawning at the beginning of summer, when temperature was increasing. Spawning of less intensity during late summer occurred when the temperature reached its seasonal peak. The gonadosomatic index correlated well with development of the species' reproductive season. The sex ratio was dominated by females (2.8:1) although sexually undifferentiated geoduck clams were the most abundant. This is the first description of the reproductive activity of P. generosa at its southernmost distribution. The results showed significant differences in gametogenic patterns relative to northern congeners, which suggest that fishery of geoducks in this region needs specific strategies.
... The increase in geoduck clam collection has led to the identification and documentation of various species worldwide. Specifically, the Pacific geoduck, Panopea generosa A. Gould, 1850, is farmed and collected 2 of 9 in the United States (USA) and Canada [8], the New Zealand geoduck, Panopea zelandica Quoy & Gaimard, 1835, is collected in New Zealand, Panopea abrupta (Conrad, 1849), is collected on a limited basis in Alaska, USA, and P. generosa and Panopea globose Dall, 1898, are collected in Mexico [9][10][11]. Therefore, these newly identified species highlight the importance of the conservation of geoduck clams worldwide and the identification of each region-specific species. ...
The geoduck clam is a high-value species in South Korea. However, the molecular and morphological characteristics of geoduck clams from the southern coast of South Korea remain unexamined. The accurate identification of native geoduck clams is crucial for their conservation and management. Therefore, this study used a combination of molecular and morphological analyses to characterize native geoduck clams from the southern coast of South Korea. Based on complete mitochondrial genome and morphological analyses, the native species of geoduck clam from this study area was identified as Panopea sp. 1. The complete mitochondrial genome sequencing of Panopea sp. 1 revealed a total of 16,225 bp in length with 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). It was also shown that Panopea sp. 1 belongs to the family Hiatellidae based on a phylogenetic analysis tree with 11 bivalve species. In particular, Panopea sp. 1 is closely related to three other Panopea species (Panopea sp., Panopea abrupta, and Panopea japonica). The phylogenetic analysis correlated with the morphological analysis. Overall, this is the first reliable record of Panopea sp. 1 in South Korea. These findings provide a basis for accurate species identification based on morphological characteristics and complete mitochondrial genome sequencing.
... P. globosa have a very short reproductive period of only 3 to 5 months (Aragón-Noriega et al., 2007; ArambulaPujol et al., 2008) and an extended resting period during which clams could not be sexed. In contrast, P. zelandica have a resting phase of only 1-2 months (Gribben et al., 2004); reproduction of P. generosa from Washington state and British Columbia is continuous with no resting period at all (Andersen, 1971; Sloan & Robinson, 1984). Population size at maturity was found to be higher than previously determined in congeners P. zelandica (55-57 mm SL Gribben & Creese, 2003) and P. generosa (58.3-60.5 mm SL; Campbell & Ming, 2003). ...
This paper describes the size at maturity of the Cortes geoduck Panopea globosa in the Gulf of California. The legal geoduck
size in Mexican fishery is 130 mm shell length (SL), which was set without knowing key biological aspects of this
species in Mexico. Geoducks were collected in two locations on the Gulf of California, in the sub-tidal zone at a depth of 10
to 25 m in January 2013. Size at 50% maturity was 88.75 mm and 89.37 mm SL in each site, respectively. The analyses of
the residual sum of squares showed both curves were not significantly different (F0.543; p < 0.5881). This study shows that
130 mm, considered the legal size, is much larger than necessary if the size at maturity was the constraining requirement
for fishing this species.
... Aquaculture of Pacific geoduck clams (Panopea generosa Gould, 1850; henceforth geoduck) is a valuable industry in Washington State and British Columbia, Canada. Geoduck clams are large, long-lived, burrowing clams found in soft intertidal and subtidal substrata from California to Alaska (Anderson 1971;Shaul and Goodwin 1982;Coan et al. 2000). Intertidal geoduck aquaculture involves high-density culture and placement of nets and polyvinyl chloride (PVC) tubes to protect outplanted juveniles from environmental stressors and predators such as crabs and birds. ...
Aquaculture operations are a frequent and prominent cause of anthropogenic disturbance to marine and estua-rine communities and may alter species composition and abundance. However, little is known about how such disturbances affect trophic linkages or ecosystem functions. In Puget Sound, Washington, aquaculture of the Pacific geoduck clam (Panopea generosa) is increasing and involves placing nets and polyvinyl chloride (PVC) tubes in intertidal areas to protect juvenile geoducks from predators. Initial studies of the structured phase of the farming cycle have documented limited impacts on the abundance of some species. To examine the effect of geoduck aquaculture on ecological linkages, the trophic relationships of a local ubiquitous consumer, Pacific staghorn sculpin (Leptocottus armatus), to its invertebrate prey were compared between geoduck aquaculture sites and nearby reference areas with no aquaculture. Mark-recapture data indicated that sculpin exhibit local site fidelity to cultured and reference areas. The stomach contents of sculpin and stable isotope signatures of sculpin and their prey were examined to study the trophic ecology of cultured and reference areas. Results showed that the structured phase of geoduck aquaculture initiated some changes to staghorn sculpin ecology, as reflected in sculpin diet through stomach content analysis. However, carbon and nitrogen stable isotopes revealed that the general food web function of sculpin remained unchanged. The source of carbon at the base of the food web and the trophic position of sculpin were not impacted by geoduck aquaculture. The study has important implications for geoduck aquaculture management and will inform regulatory decisions related to shellfish aquaculture policy.
... Predation risk is very high during early benthic life (Goodwin and Shaul 1984) but decreases quickly after the age of 1 year (Sloan and Robinson 1984). Predation on adult geoducks has been generally considered rare under normal circumstances (Andersen 1971;Fyfe 1984). In recent years, however, predation by sea otters (Enhydra lutris) appears to have increased along the west coast of Vancouver Island, where the ranges of the two species overlap (Underwater Harvesters Association 2001). ...
Geoduck (Panopea abrupta) stocks are perceived as stable and their fisheries as sustainable, but this may reflect a mismatch between slow-paced dynamics (maximum recorded age 168 years) and short-term perception. Management is based on biological reference points, whose appropriateness as a means to ensure sustainability is limited by a sedentary lifestyle and long-term trends in productivity. Analysis of age frequency distributions for 19791983, postharvest recovery rates measured in Washington in tracts pulse-fished during the 1980s and 1990s, and age frequency distributions compiled in British Columbia during the 1990s consistently suggest that recruitment declined for decades (long before the onset of the fishery), reaching a minimum around 1975, and rebounded afterwards. In such scenario, reliance on biological-reference-point-based harvest rules without timely feedback could accelerate population declines, eventually driving an apparently sustainable fishery to collapse. The merits of approaches that rely on monitoring and feedback using data-driven decision rules are stressed. Transition from a biological-reference-point-based strategy to one based on monitoring and feedback will demand a shift in research focus to the design of practical monitoring programs and the evaluation of management procedures by means of simulations. For geoducks and other long-lived organisms, monitoring should integrate data informative at different temporal scales.
... Compared with other geoduck populations of P. generosa and P. zelandica at higher latitudes, this environmental constraint entails a more protracted nonreproductive period (up to 7–8 mo) (Arago´nArago´n-Noriega et al. 2007; Caldero´nCaldero´n-Aguilera et al. 2010), during which energy can be directed to somatic growth. In contrast, samples of P. generosa from the Pacific coast of Baja California show a pattern of partial protracted spawning during the year (Calderon-Aguilera, unpublished results) comparable with those of conspecifics at higher latitudes (Andersen 1971, Sloan & Robinson 1984 ). Such differences in life history attributes, which are likely related to their deep evolutionary divergence (see discussion in the next section), in concert with differences in physical and biological environmental variables between the coastal Pacific and the Gulf of California habitats (Sandoval-Castillo et al. 2004 ) are likely responsible for the phenotypic interspecific differentiation. ...
Geoduck clams have become the most profitable emerging fishery resource in Northwest Mexico, with profits of more than US$30 million during the last few years. The fishery targets two species—Panopea globosa in the Gulf of California and Panopea generosa on the Pacific coast of Baja California—but is managed indistinctively. Despite its growing importance, scientific research on the basic biology of the Mexican stocks has been inexistent until recently. A major gap in knowledge is the interspecific distinction in structural and functional biological attributes. Consequently, the aim of this article is to provide the biological basis of phenotypic (morphometric) and genetic distinction between P. globosa and P. generosa to assist in their management and conservation. We found that P. generosa from the Pacific coast of Baja California is significantly smaller than P. globosa from the northern Gulf of California in shell length, width, and height (t-tests, P < 0.0001), and that shell width and height scale differently to length in both species. Multivariate analyses (multidimensional scaling) provided additional support (stress = 0.04) to the species and geographical distinction. Genetic data from the nuclear ribosomal DNA provided contrasting results between polymerase chain reaction– restriction fragment length polymorphisms and direct sequencing. Ribosomal DNA sequences revealed higher diversity (haplotype and nucleotide) in P. globosa. Standing in sharp contrast with the low intraspecific divergence, was the very large genetic differentiation between species in excess of 20% corrected Kimura 2-parameter sequence divergence and accounting for 98% of the molecular variance of both species. This differentiation was found to be of consequence for novel methods of molecular species identification and for the interpretation of the phylogeography and evolution of Panopea in the North Pacific. The relevance of our findings goes to the heart of filling a major information gap pertaining to the distinction of both species. Scientific and lay stakeholders of these valuable resources need to ascertain and acknowledge this distinction to adopt sustainable management and exploitation practices.
... Free-spawning March-July (Andersen 1971), producing planktotrophic larvae that settle after 3-5 wk (Goodwin and Bease 1989). Sexual maturity reached in 3-4 yr at a shell length of 100 mm (Washington Department of Fisheries/Washington Department of Natural Re sources 1985). ...
The Pacific geoduck, Panopea generosa, is an ideal candidate to investigate
patterns of life history variation and morphological plasticity in shell shape, as it occurs
over a large geographic range, inhabits different marine environments, and experiences
intense fishing pressure in some locations (i.e., Mexico and Washington). Six
populations were sampled from Washington to Mexico to evaluate evidence for
geographic variation in demography, life history, and morphology. Results provided
evidence for a latitudinal cline with larger clams occurring in locations characterized by
colder water temperature. Age structure and longevity analyses indicated that life
expectancy was significantly lowered at intertidal sites compared to subtidal sites,
potentially in response to fishing. Von Bertalanffy growth model (VBGM) analyses
revealed significant spatial variation in asymptotic lengths across sampling locations.
Correlations of climate (temperature and chlorophyll a) and growth parameters indicated
that clams reached larger sizes at locations that were cooler and more productive.
Morphological analyses revealed significant spatial differences that did not follow a
latitudinal pattern, but may be better explained by site-specific habitat differences.
Results will aid managers in developing regulations, tuned to the demographic variability
present along the eastern Pacific coast.
This paper describes the size at maturity of the Cortés geoduck Panopea globosa in the central Gulf of California. The objective of this study was to determine the size at which 50% of the population is mature. The justification is that this value is still unknown not only of this particular species, but in general, for other species of the genus such knowledge is scarce. Another justification for the study is that the minimum legal size in Mexican Cortés geoduck fishery, which is 130 mm in shell length (SL), was determined ignoring key biological aspects of the species in Mexico. Mexican geoducks were collected sub-tidal, 20 m to 25 m depth in Bahía Guaymas-Empalme, Sonora located in the Central Gulf of California in January 2014. A logistic model was used fit with the maximum likelihood criterion to get the size value at 50% maturity, which was 91.906 mm SL and 90.909 mm SL, female and male respectively. The analyses of the residual sum of squares showed both curves were not significantly different (F0.284; p
Establishing priorities associated with maintaining healthy ecosystems and viable fisheries under climate change is a challenging task facing resource managers with limited resources. This study adapted a climate change risk framework developed and used in Australia and applied it to 43 west coast Vancouver Island (WCVI) marine species to assess their sensitivity to climate change. Subsequently, local experts completed the same framework for 6 of these same species, and a short survey was completed as an additional comparison of 14 of the species. Species information assembled from literature for each of 12 attributes was assigned to one of three risk categories. Average risk scores were compiled for each species and compared among species groups, trophic levels and life history strategy types. Based on the literature derived assessment, elasmobranchs were most sensitive to climate change, while flatfishes were the least. The mid-trophic level and ‘periodic’ life history type were assigned the lowest risk score of their categories. Expert responses were insufficient to evaluate the validity of all the results. However, expert assessments differed from those found by the literature-based assessment in most instances. In the case of Pacific herring, the risk score of the expert-based assessment was much higher. In addition to expert review, a short survey conducted in conjunction with this study revealed that the literature-based assessment did not capture important pieces of local ecological information (i.e. connectivity, seasonality) that appear to be important in assessing species’ sensitivity to climate change. Weaknesses with applying the Australian framework to WCVI species were identified; suggestions for improvement included rescaling or redefining attributes that consistently scored low or high. In conclusion, results from literature surveys are a useful starting point when assessing species’ sensitivity to climate change. However, when used in isolation they may produce misleading rankings and need to be augmented by expert judgement and specific local information to be confident in the results.
The effect of ration on Panopea generosa gonad development was tested over 52 days. Clams were fed Isochrysis sp. and Chaetoceros muelleri (50 : 50 cell count) at rations of 0.8 × 109, 2.4 × 109, 4.0 × 109, 5.6 × 109, 7.2 × 109 and 10.0 × 109 cells clam−1 day−1 (R1, R2, R3, R4, R5 and R6, respectively). The highest ration (R6) caused a 25% die-off within 3 days and was discontinued. Ration did not significantly affect condition index, gonadosomatic index, connective tissue occupation index or oocyte diameter. Clams fed the R5 ration (85% of which spawned from day 26 to 52) were more spent than clams in any other treatment with significantly fewer oocytes mm−2 than those fed the R1, R2 and R3 rations and significantly lower levels of sperm occupation than clams fed any other ration. Spawn percentages were low from day 26 to 52 in R1, R2 and R4 (15, 0 and 0%, respectively). Clams in the R3 treatment had a similar spawn percentage (100% from day 26 to 52) to those in the R5 treatment yet maintained gonads in a more ripened condition with higher levels of gamete occupation, making R3 the most likely ration to maximize gamete output over time.
This paper describes morphometric relationships, and the timing of gametogenic development and spawning for the geoduck clam Panopea globosa (Dall 1898) from a population in the east central Gulf of California. Clams were collected monthly for a year (October 2004 to October 2005), and were measured and weighed to obtain morphometric relationships. Standard histological analysis and measurements of oocyte diameters were used to describe the timing of gametogenic development and spawning. Most morphometric variables were significantly correlated, however the coefficients of determination were generally low (<0.5) indicating high variation in measured traits. Early gametogenic development was observed in late summer/autumn when SST was high (30°C). Development increased as water temperatures fell with ripe individuals observed in early winter (20°C). Spawning occurred between January and February (winter), when SST were at their coolest (18°C). Cytological characteristics of the gonad and averages of oocyte diameters for the different reproductive phases were similar to other geoduck species previously described. Overall sex ratios were equal. This study is the first ecological study to be conducted for P. globosa. Given the development of fisheries for P. globosa and the interest in developing aquaculture for this species, the data provide valuable information for fisheries managers and aquaculturalists and represent the basis for further research on this species.
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