Indian Journal of Geo-Marine Sciences Vol. 42(2), April 2013, pp. 201-205

Age and growth of the Cortes Panopea globosa (Dall, 1898) in the upper Gulf of California

S. A. Pérez-Valencia1,2 & E. A. Aragón-Noriega2* 1 Centro Intercultural de Estudios de Desiertos y Océanos, A.C. Edif. Agustín Cortez Col. Las Conchas, Puerto Peñasco, Sonora 83550, Mexico. 2Centro de Investigaciones Biológicas del Noroeste, Unidad Sonora. Km 2.35 Camino al Tular, Estero Bacochibampo, Guaymas, Sonora 85454, Mexico [E-mail : [email protected]]

Received 20 September 2011; revised 7 September 2012

This study first describes the age and growth of the cortes geoduck Panopea globosa in the upper Gulf of California. Ages were from 2 to 34 years old but mode was 11 and 12 y. Average size was 146±3 mm shell length. According to the VBGM, the asymptotic length of the shell in cortes geoduck P. globosa off Puerto Peñasco (located in the upper Gulf of California) was 163.88 mm and the growth coefficient (k) was 0.17. It is recorded a P. globosa of 34 y old and the nearest was another individual 22 y. This shows that cortes geoduck from the upper Gulf of California is a recently settled populations. Being a recently detected species this information become important for biological knowledge and for managerial purpose as fishery.

[Key words: fisheries, environment, bivalve]

Introduction that gametogenic development starts in early autumn, Commercial fisheries of the geoduck clams have when Sea Surface Temperature (SST) is ∼30°C while been appearing during the last four decades in many spawning occurred in winter when SST is ∼18°C. parts of the world. For example, Panopea generosa A dditionally8 establish that gametogenesis it’s trigged by (Gould, 1850) formerly (Conrad, a strong decrease in temperature (>3°C). They propose8 1849) is captured since 1970 in Washington State, that this synchronic and short period of gametogenesis 1 2,3 USA and 1976 in British Columbia, Canada , might be clarified by the conceptual planktonic larval Panopea zelandica (Quoy & Gaimard, 1835) since development model9, which explains that this strategy 4 1988 in New Zeeland , and Panopea abbreviata allows spawning to occur when ideal feeding conditions 5 (Valenciennes, 1839) since 1999 in Argentina . In (highest phytoplankton production) for larvae are Mexico this fishery is even a more recent. Although present in the area. They also give account of the people involve in their commercialization affirm that differences between P. globosa and others species like captures begun in 2000, official landings records go P. abrupta and P. zelandica which gonad development back to 2002. Total catch have grown fast (Fig. 1) and last 10–12 months, starts when water temperatures are recent surveys suggest a wide distribution of beds low and spawn as water temperatures rises. Recently along the both coast of Baja California and on the genetics studies10 have established that two species, coast of Sonora in Mexico, and therefore, an increase P. globosa and P. generosa are captured in Baja in landings is feasible. California peninsula (Gulf of California and Pacific Specific knowledge about the biology and ecology of coast respectively, Fig. 1), but accurate distribution Panopea spp. in Mexico it’s now been generated. limits for both species still to be defined. To date there are five peer review papers of Panopea One of the main topics in fishery ecology is the spp in Mexico. Three studies for P. globosa in the east study of individual growth because it gives insights central and upper Gulf of California6,7,8 determined by about population dynamics of species, like the growth histological analysis, that sex ratios were equal and and mortality rates and other parameters that are ———————— commonly used on stocks assessments and other *Correspondence 11,12 [E-mail: [email protected]] life-history studies . Mexican fisheries authority 202 INDIAN J. MAR. SCI., VOL. 42, NO. 2 APRIL 2013

Fig. 1—Historic capture of Panopea generosa (Canada and U.S.A.) Fig. 2—Sampling area. Panopea globosa bed (solid line) where the and Panopea spp. (México). Source: NOAA Fisheries, Office experimental fishing is authorized. Dashed lines are bathymetry of Science and Technology; Fisheries and Oceans Canada; Subdelegación de Pesca, Ensenada, B.C.; CRIP-La Paz; CEDO fresh water contribution comes occasionally from the Intercultural, A.C Colorado River. UGC comprised of triangular area of (CONAPESCA) attempts to pursue a conservative 5,000 km2 within the limits of an imaginary line approach in regulating the fishery by imposing a between the town of San Felipe, Punta Borrascoso minimum legal size of 130 mm shell length. It is an and the old mouth of the Colorado River (17Lavín arbitrary reference point, following the precautionary et al. 1997). approach for responsible fisheries established by UGC is relatively shallow, with a maximum depth FAO. Nothing is known about the growth rate of of 30 m and an average depth of 15 m. Irregular P. globosa in the Gulf of California. However, this bathymetry is characterised by channels and low knowledge is required for determining sustainable elongate, flat-topped bars parallel to the coast that harvest strategies and to address the biological basis extend from the mouth of the river ~50 km to the and the suitability of minimum size as a management southeast (18Alvarez & Jones 2002). Climate is strategy. continental desert with little rain (85 mm annual For geoduck clams the common approach to average). Highest air temperature in summer is estimate age has been counts of internal growth bands ~40oC. Region is an inverse estuary, characterised by because early and older rings are clearer and easier to hypersaline water and associated gravity currents, identify compared with external rings counts1. Mainly which arise in arid regions where there is little method consists in cross section of the shell and acetate precipitation or runoff and a high rate of evaporation peel, and has been used for P. generosa in U.S. and (18Alvarez & Jones 2002). Canada1,13,2,14, for P. abbreviata in Argentina5 and for 4,15 Clams were collected during fishery independent P. zelandica in New Zealand . The only growth study surveys made from November 2008 to October 2009 in Mexican geoduck clams was taken out in Pacific 16 as part of an experimental fishery in Puerto Peñasco, coast with P. generosa . These previous studies have Sonora, Mexico (Fig. 2). Sampling was made with a successfully used the von Bertalanffy growth model panga (small, fiberglass open fishing boat equipped VBGM to estimated growth parameters. Present with an outboard motor) and by commercial hookah investigation is to determine the growth parameters of divers using a stinger (high-pressure water yet used the cortes geoduck in the upper gulf of California, by to unburied the clams). Collected organisms were means of the BVGM and contribute to sustain the tagged and weighted alive and then the body was managerial strategy of the 130 mm legal size. removed from the shells. After dried out, shells Materials and Methods were weighted to the nearest 0.1 g and shell length UGC is located in the northern part of the Gulf of (straight line distance between the anterior and California, Mexico, between 31º00' and 31º36' N and posterior margins of the shell) was measured to the 114º50' and 113º48' W (Fig. 2). The only significant nearest 0.1 mm using a calipers. PÉREZ & ARAGÓN : AGE AND GROWTH OF THE CORTES GEODUCK 203

Right valves were aged following the acetate peel averaged 146±3 (SD) mm with a mode of 157 mm method described1. This procedure has been used (Fig. 3). More than hundred clams were in the range previously13,2 and reviewed and validated19. It consists 140 to 169 mm SL. in making and impression of the internal growth Age ranged from 2 to 34 years, with the oldest rings from a polished surface of the hinge cut it being an unsexed 169 mm long and the transversally. But in our case, the clorhidric acid stays youngest clams were 2 years old unsexed of 85 mm for a minute in the cut face of the shell because shell SL. Largest clam (198 mm SL) was a 20 years that proofs to give clearly peelings. Count growth old unsexed. Age frequency histogram (Fig. 4) shows band from peelings using a Carl Zeiss microscope that the 11 and 12 year clams were by far the following a cross-dating technique20. For obtaining strongest mode in the distribution of ages. precise age estimation, growth increments were The resulting growth curve is shown in Fig. 5. Size confirmed by counting it by two readers. Readers at age data show that shell growth is rapid during receive training twice by personnel of Fisheries the first 10 years and then decreases dramatically, and Oceans Canada Fish Ageing Laboratory, Pacific becoming very slow for individuals older than Biological Station at Nanaimo, British Columbia, 15 years. Asymptotic length (L∞) of the shell was Canada. 163.88 mm and the growth coefficient (k) was 0.17. The growth model selected was the von Bertalanffy growth model (VBGM). It is given by the equation, − − k(t t0 ) L(t) = L∞ (1 − e ) + ε Were; L(t) is length of the shell (LS) at age t.

L∞ is the mean length of very old organism (asymptotic length parameter). k determines how fast L∞is reached (curvature parameter). t0 is the hypothetical age when the organism had zero length (initial condition parameter). ε ∼ σ 2 1 N (0, 1 ) is the error structure.

The model was fitted by maximum likelihood. Additive error structure was considered. The Fig. 3—Length frequency right valve aged of Panopea globosa maximum likelihood fitting algorithm was based on the equation  n  Φ data/(LL ) −=   +σ∗+π )1)(Ln2)2(Ln(  2  where Φ represents the parameters of the models and 5 represents the standard deviations of the error calculated by the following equation:

2 − = Results A total of 157 right valves were measured and aged following the acetate peel method. Large number of unsexed precluded separate analysis by sex. Geoduck shell length SL ranged from 85 to 198 mm, Fig. 4—Age frequency of 157 organism of Panopea globosa aged 204 INDIAN J. MAR. SCI., VOL. 42, NO. 2 APRIL 2013

In this study P. globosa asymptotic length was found to be 163.88 mm SL using VBGM. Being the first study dealing with growth parameter, there is no way to compare same species, but congener. This asymptotic length is within the range found for P. generosa and in Washington State of 132 to 173 mm23. But quite larger than others found in the Baja California peninsula, where estimated the asymptotic length in P. generosa as 135 mm16 SL. And those found in British Columbia of 129 to 147 mm2,21,14. On the other hand, P. globosa asymptotic length is larger than other species of from the southern hemisphere: 106 mm SL for P. abbreviata5 and 116 mm for P. zelandica15.

One purpose of this study was to investigate Fig. 5–Growth curve adjusted to length at age data of 157 whether the 130 mm SL established as legal size had organism of Panopea globosa from Puerto Peñasco biological meaning. As found in this field study, the asymptotic length is reasonably larger than 130 mm, Discussion and therefore the size limit would seem to be suitable This is the first report on the growth studies in in this fishing zone. This is contrary to the P. globosa from the upper Gulf of California and conclusions determined that for P. generosa in the being endemic is the first one around the world. Pacific coast off Baja California this management However, P. globosa populations in Gulf of strategy does not work16. Moreover, an adult geoduck California are the target of a fast growing fishery is incapable of reburying itself if removed from the and an understanding of population parameters is substrate, since the digging appendage is vestigial in required to develop sustainable harvest strategies. the adult24. Is important to clarify that this finding Acetate peel technique to count growth rings apply only for P. globosa from the upper Gulf of for geoduck age estimation was initially validated by California and would be required the make growth 1 two separate methods and was used to determine studies in central and south part of the Gulf of 2,21 P. generosa age in British Columbia , Washington California where fishing areas are starting to be an 22 4 State , P. zelandica in New Zealand and P. abbreviata important fishing beds. 5 in Argentina . Further validation of the method has Some authors claimed23 that the growth constant recently been demonstrated by using cross-dating k in the von Bertalanffy model is the key parameter techniques, first developed by dendrochronologists, in estimating fishing mortality rate. In this study, we which looks for synchronous growth patterns within found k=0.17, which is intermediate to those a sampled population and utilizes ‘signature years’ to estimated in Washington state (0.113–0.235)23, and 19 cross-reference between specimens of a sample . among those found in Canada14 (0.146 and 0.189). Signature years were clearly identified and consistently In this case, the k parameter is also similar to that used for cross-dating and ageing of the Baja found for the southern hemisphere geoduck: 0.183 in 16 California geoducks . There is no reason to suspect P. abbreviata5 and 0.16 in P. zelandica4. Higher that internal growth ring deposition does not occur estimation of k is expected when target populations yearly in the upper Gulf of California. are composed of younger individuals23. This is There are many examples of P. generosa aged over important in the comparison of P. globosa and 100 yr1,13,14. And in the southernmost extent in its congeners because young individuals were found in geographic distribution, off Baja California16 found this study (mode 10-12 y old) and the k parameter is a 96 yr old individual of P. generosa. In this study, also similar to older population of P. generosa in we found a P. globosa of 34 yr old and the nearest Canada and U.S.A. was another individual 22 yr. This shows that cortes Present study recorded that the asymptotic length geoduck from the upper Gulf of California is a of the shell in cortes geoduck P. globosa off Puerto recently settled populations. Peñasco (located in the upper Gulf of California) was PÉREZ & ARAGÓN : AGE AND GROWTH OF THE CORTES GEODUCK 205

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