- Split View
-
Views
-
Cite
Cite
Gustavo A. Lovrich, Mario Perroni, Julio H. Vinuesa, Federico Tapella, Alejandro Chizzini, M. Carolina Romero, Occurrence of Lithodes Confundens (Decapoda: Anomura) in the Intertidal of the Southwestern Atlantic, Journal of Crustacean Biology, Volume 22, Issue 4, 1 October 2002, Pages 894–902, https://doi.org/10.1163/20021975-99990301
- Share Icon Share
Abstract
We provide the first biological data for the southern king crab Lithodes confundens, found intertidally on the Atlantic coast of southern South America (51°21′S–54°20′S). Between October and December 1997 and in December 1999, specimens were found during the ebbtide in crevices of the wave abrasion platform. The size of animals progressively increased from |$\sim 50 \ {\rm mm}$| carapace length (CL) in October to |$\sim 105$| and 75 mm CL in December for males and females, respectively. The sex ratio increased from October to December, from 1:1 to 2:1 male : female. Females molted during December. A total of 61 mating pairs were found at Bahía Grande (51°21′S, 69°02′W), between 16 November and 28 December 1997, and represented 31% of a total of 399 captures. Mating pairs were in precopulatory embrace, which was formed by a male in intermolt condition and a female in ecdysis. The male was always larger than the female. The relative growth of the male right chela was studied with the MATURE computer routine for two different chela dimensions, length and width. Slopes of relationships between chela sizes and CL changed at 89.8 and 87.3 mm CL, respectively. The estimated size of physiological maturity for 82 females was 68.3 mm CL. The smallest male participating in mating pairs was 75.2 mm CL. We suggest 100 mm CL as the legal size for fishery management purposes.
Resumen
Se presentan los primeros datos biológicos para la centolla Lithodes confundens, que fueron encontrados en el intermareal de la costa atlántica del extremo austral de Sudamérica (51°21′S–54°20′S). Entre octubre y diciembre de 1997 y en diciembre de 1999, se encontraron especímenes durante las bajamares, asociados a grietas de la plataforma de abrasión de ola. El tamaño de los animales encontrados aumentó progresivamente, de |$\sim 50 \ {\rm mm}$| de largo de caparazón (LC) en octubre hasta |$\sim 105 \ {\rm y} \ 75 \ {\rm mm}$| LC en diciembre, en machos y hembras, respectivamente. La proporción sexual aumentó de octubre a diciembre de una relación 1:1 a 2:1 machos : hembras. Las hembras mudaron en el intermareal durante diciembre. Un total de 61 parejas en acoplamiento fueron encontradas en Bahía Grande (51°21′S, 69°02′W), entre el 16 de noviembre y el 28 de diciembre de 1997, y representaron el 31% de los 399 animales capturados. Las parejas en acoplamiento estaban en el abrazo precopulatorio, y constituidas por un macho en condición intermuda que siempre fue más grande que la hembra, que estaba en proceso de ecdisis. En los machos, el crecimiento relativo de la quela derecha fue estudiado con la rutina “MATURE”, para las dimensiones largo y ancho de la quela. Las pendientes de las rectas definidas entre los tamaños de la quela y el LC cambiaron a los 89,8 y 87,3 mm LC, respectivamente. La talla de madurez fisiológica, estimada a partir de 82 hembras, fue 68,3 mm LC. El macho más pequeño participando en una pareja fue de 75,2 mm LC. Para un futuro manejo de la pesquería, sugerimos una talla legal de 100 mm LC.
Near the southern tip of South America, nine lithodid species are known to occur: Neolithodes diomedeae (Benedict, 1894); Lithodes santolla (Molina, 1782), formerly L. antarcticus Jacquinot, 1853; L. confundensMacpherson, 1988; L. turkayiMacpherson, 1988; Paralomis granulosa (Jacquinot, 1847); P. spinosissima Birstein and Vinogradov, 1972; P. formosa Henderson, 1888; P. anameraeMacpherson, 1988; and P. birsteiniMacpherson, 1988. By contrast, only two lithodids are known to occur in Antarctic waters of the Belinghausen Sea: L. murrayi Henderson, 1888, and P. birnsteini (see Klages et al., 1995; Arana and Retamal, 1999). Knowledge of lithodid biology has broadened because of economic interest in the crabs as new fisheries developed (e.g., Hoggarth, 1993; Otto and MacIntosh, 1996; Lovrich, 1997; Watters and Hobday, 1998; Lovrich and Vinuesa, 1999). Until recently, L. confundens was known only from its original description (Macpherson, 1988). Particularly, L. santolla and L. confundens could have been misidentified because of their morphological similarities, their probable geographical overlap, and the relatively recent description of the latter as a new species (cf. Macpherson, 1988). Thus, some reports on the biology of L. santolla occurring in the Strait of Magellan or coastal southwestern Atlantic likely refer to L. confundens (e.g., Angelescu, 1960; Scelzo, 1974).
Macpherson (1988) first described L. confundens from nine specimens captured off Islas Malvinas (Falkland Is.), near the Burwood Bank, and one from the Strait of Magellan (Fig. 1). The depth distributional range of the specimens was then reported between 50 and 119 m depth (Macpherson, 1988). In Bahía Grande, L. confundens arrives in the intertidal mainly during summer, and crabs have been harvested occasionally since the 1950s. At that time, the landed species was identified as L. santolla (= L. antarcticus Jacquinot, 1844), but a drawing of the crab spinulation pattern shown by Scelzo (1974) and photographs provided by Angelescu (1960) allow us to identify this species as L. confundens. If these authors had sampled L. santolla mixed with L. confundens, they might have noted it and reported their morphological differences. However, L. santolla from Golfo San Jorge and the Beagle Channel have some distinctive characters (Vinuesa, 1985). Specimens from Golfo San Jorge have pink coloration, shorter spines, and gastric and cardiac regions of the carapace flatter than those from the Beagle Channel. Lithodes confundens is similar to L. santolla from Golfo San Jorge in the aforementioned characters, and hence this circumstance could have contributed to their misidentification.
Historically, the mixed fishery for L. santolla and P. granulosa in the Strait of Magellan and other channels has been the most important crab fishery in southern South America, and yields have peaked to |$\sim 3,000 \ {\rm t} \cdot {\rm y}^{-1}$| per species (Lovrich, 1997). However, fisheries for any lithodid crab off the Atlantic coast of southern South America have been sporadic. Between the 1950s and 1970s, landings of reportedly L. santolla from a tangle-net fishery at the intertidal of Bahía Grande, Province of Santa Cruz, varied between 3,000 and 9,000 crabs, i.e., approximately 3 t and 5 t per season from December to February (Scelzo, 1974). In 1972, 11 t of reportedly L. santolla were harvested during three weeks off Bahía Grande by means of tangle nets deployed at 6–71 m depth (Boschi, 1997). During 1993–1996, and owing to the collapse of the L. santolla fishery of the Beagle Channel, an intermittent trap-fishery for apparently L. confundens developed off Tierra del Fuego, near Río Grande (Fig. 1). Landings peaked at 32 t in 1995, |$\approx 49\%$| of the total landings of Lithodes spp. of the Province of Tierra del Fuego (Lovrich, 1997). Currently, these activities are considered as sport or subsistence fisheries because extraction is realized by people looking for recreation or by unemployed people seeking some income, respectively. However, because of low yields of the Beagle Channel fishery, L. confundens fisheries off the Provinces of Santa Cruz and Tierra del Fuego are expected to develop.
In this article, we studied L. confundens that occurs in the intertidal in summer and provide estimates for sizes at maturity and composition of mating pairs. We also discuss the geographical distribution of L. confundens in relation to its closely related species, L. santolla.
Materials and Methods
The sampling site was a beach of Bahía Grande at Monte Tigre (Fig. 1; 51°21′S, 69°02′W), in the Province of Santa Cruz, Argentina. In southernmost South America, i.e., south to 40°S, the Atlantic coast is characterized by prominent cliffs that are eroded by waves. At Bahía Grande during spring tides, a beach of approximate 1–1.5 km is exposed. This beach has three distinct sections: the first 50–150 m near the cliff’s base is steep and of gravel; the following |$\sim 200\hbox{-}\!\hbox{-}300 \ {\rm m}$| is subhorizontal and of fine sand; and in the last 700–800 m, outcrops of sedimentary rocks form a wave abrasion platform, containing crevices and tidal pools between 0.2 to 2 m depth. These outcrops alternate with sand bars 5–100 m wide that are perpendicular to the coastline. The tidal regime is semidiurnal, with an average and maximum tidal amplitude of |$\sim 8$| and 13 m, respectively (Anonymous, 1997). Spring tides are more pronounced between December and March.
In Monte Tigre, sampling was carried out during spring tides of September–December 1997 and in December 1999. Crabs were captured during ebbtides by inspecting the sandy beach, draining crevices, or beneath the rocks at the abrasion platform. Additionally, a tangle net of 0.12 m of mesh and 40 m long was placed in a fixed location of the beach, so that it was completely exposed |$\sim 2 \ {\rm h}$| before low tide. The net was inspected at every low tide, i.e., twice a day. As a measure of catch per unit effort (CPUE), crabs from the net were enumerated. For each crab, we recorded sex, presence of eggs or postovigerous setae, carapace condition, and participation in mating couples. Postovigerous setae were darkened pleopod setae with rests of egg capsules and indicated that a female had brooded eggs. Carapace condition was determined by judging the degree of epibiosis and hardness to the touch, according to the scale of Lovrich and Vinuesa (1993). Carapace length (CL) was measured in all animals and in exuviae found on the beach. In December 1997, male chela length and width were also measured. All measurements were done with a dial caliper with 0.1 mm precision.
Because Monte Tigre is inaccessible by road during February–August and to ensure a sampling of the intertidal all year long, additional inspections were made along the Atlantic coast of Tierra del Fuego, between 53°35′S and 54°20′S. Previous occurrences of lithodid crabs at the intertidal of these locations had been reported by fishers. Sampling was done during 30–31 January, 28 February, 27 March, 5 May, 23 July, 8–9 September, and 4 December 1998. Because fishers gathered all the available animals, we identified crabs only to the specific level.
Lithodes confundens was distinguished from L. santolla on the basis of the carapace spinulation pattern described by Macpherson (1988). Particularly, we found most useful the following characters: (1) Each branchial region with 30 small spines vs. 15–20 spines in L. santolla. (2) Most individuals of L. confundens with a row of three or four spiniform granules between the two rows defined by the four cardiac spines (cf. plate 12B, Macpherson 1988). (3) Behind the posterior pair of cardiac spines, L. confundens with two pairs of spiniform granules vs. a sole medial spine in L. santolla. (4) The anterior projection of the carapace and between the two dorsal pairs of spines, all L. confundens with a single small spine that is lacking in L. santolla. Macpherson (1988) noted that only some individuals of his material had this spine.
In brachyurans and anomurans, the change in relative growth of the chela is considered the attainment of secondary sexual characters (Hartnoll, 1978) and is the so-called “morphometric maturity” (see Sampedro et al., 1999, for a review). In male L. confundens, the size at change in the slope of the relationship between the right chela and CL was calculated using the computer routine MATURE1 (Somerton, 1980). Two different chela dimensions—chela length and height—were evaluated. Values of “juvenile” and “adult” bounds required by the routine are CL-sizes below and above which the relative growth rate is constant, respectively. Bounds were chosen by judging the scatterplot of chela size versus carapace length (Fig. 2) and were established at 75 and 100 mm CL, respectively. Measurements of partially regenerated chelae were excluded from this analysis. In females, the size at physiological maturity was calculated by fitting the proportion of ovigerous females in 5-mm CL size classes to a logistic curve by the method of least squares. The intersection between the ordinate at 50% and the calculated logistic equation provided the average size at physiological maturity (Wenner et al., 1974).
Standard statistical analyses were performed according to Sokal and Rohlf (1995) as indicated in the text. When required, conditions of data homoscedasticity and normality were tested.
Results
Lithodes confundens occurred in the intertidal off Monte Tigre, Santa Cruz, from October to December and in the Atlantic coast off Tierra del Fuego in December and January. A total of 909 and 156 crabs were found at Monte Tigre and the Atlantic coast of Tierra del Fuego, respectively. All specimens found at both locations were L. confundens. Results presented hereafter are from Monte Tigre.
In Monte Tigre, crabs were found associated with crevices of the wave abrasion platform. Animals began to abandon their refuges and walked downstream at ebbtide when at crevices water drained relatively fast |$(\sim 2\hbox{-}\!\hbox{-}4 \ {\rm m} \cdot {\rm s}^{-1})$|, and the water depth was approximately 0.2 m. In some cases, animals found another crevice in which to shelter, but if not, they were collected on sand bars adjacent to the abrasion platform. In many observations of mating couples, males abandoned the females, which were in pre- or postmolt condition, and females were killed by gulls, Larus dominicanus. However, if the tidal pool was deep enough, animals may have remained undetected because of the high turbidity of water. The seven samplings with the tangle net captured on average 0.24 |$(\pm \ 0.15)$||${\rm crabs} \cdot {\rm m \ net}^{-1} \cdot {\rm tide}^{-1}$|.
For 176 male L. confundens, estimates of the carapace lengths that correspond to changes in the chela allometry were 89.8 and 87.3 mm CL for the chela length and width, respectively (Table 1, Fig. 2). The calculated fitting error was about 1% in both cases. For both chela dimensions, the slope of the linear regression of “juvenile” males was significantly less |$(F_{{\rm height}} = 34.8; \ F_{{\rm length}} = 19.1; \ P \lt 0.001)$| than that for “adult” males (Table 1). The estimated size of physiological maturity for 82 females was 68.3 mm CL. Among the 54 females in ovigerous or postovigerous condition, only two were carrying eggs, and the others were postovigerous. The smallest postovigerous female was 62.5 mm CL.
Variable . | Size at allometric change . | Fitting error . | Regression . | |
---|---|---|---|---|
“Juvenile” . | “Adult” . | |||
|$\log_{10}$| Chela length | 89.8 | 0.89 | |$-0.73+1.057\log{\rm CL}$| | |$-0.71+1.074\log{\rm CL}$| |
|$\log_{10}$| Chela height | 87.3 | 0.92 | |$-2.22+1.20\log{\rm CL}$| | |$-3.88+1.60\log{\rm CL}$| |
Variable . | Size at allometric change . | Fitting error . | Regression . | |
---|---|---|---|---|
“Juvenile” . | “Adult” . | |||
|$\log_{10}$| Chela length | 89.8 | 0.89 | |$-0.73+1.057\log{\rm CL}$| | |$-0.71+1.074\log{\rm CL}$| |
|$\log_{10}$| Chela height | 87.3 | 0.92 | |$-2.22+1.20\log{\rm CL}$| | |$-3.88+1.60\log{\rm CL}$| |
Variable . | Size at allometric change . | Fitting error . | Regression . | |
---|---|---|---|---|
“Juvenile” . | “Adult” . | |||
|$\log_{10}$| Chela length | 89.8 | 0.89 | |$-0.73+1.057\log{\rm CL}$| | |$-0.71+1.074\log{\rm CL}$| |
|$\log_{10}$| Chela height | 87.3 | 0.92 | |$-2.22+1.20\log{\rm CL}$| | |$-3.88+1.60\log{\rm CL}$| |
Variable . | Size at allometric change . | Fitting error . | Regression . | |
---|---|---|---|---|
“Juvenile” . | “Adult” . | |||
|$\log_{10}$| Chela length | 89.8 | 0.89 | |$-0.73+1.057\log{\rm CL}$| | |$-0.71+1.074\log{\rm CL}$| |
|$\log_{10}$| Chela height | 87.3 | 0.92 | |$-2.22+1.20\log{\rm CL}$| | |$-3.88+1.60\log{\rm CL}$| |
A total of 61 mating pairs were found between 16 November and 28 December 1997, and they represented 31% of a total of 399 captured crabs. Eighteen mating pairs were captured with tangle nets. Mating pairs were formed by a male in intermolt condition that was always larger than the female (Fig. 3A). Mating pairs collected along the sand bars or from crevices were in precopulatory embrace; the male grasped the female by the meropodite of both chelipeds in a face-to-face position. In pairs caught by tangle nets, males grasped females by at least one cheliped. Of all grasped females, 55% were in pre- or postmolt conditions, and the smallest female found was 60.2 mm CL. The size of males was proportional to the size of females |$(F = 18.1; \ P \ \lt \lt 0.001)$| and explained 23.5% of the variation in female size (|$R^{2} = 0.235$|; Fig. 3A). The smallest male that participated in mating pairs was 75.2 mm CL. Overall, 24.5% of males larger than 75 mm CL participated in pairs (Fig. 3B). The maximum proportion of mating males occurred at the 95 mm CL size class, and at the 105 and 110 mm CL size classes, more than 30% of males were paired (Fig. 3B).
The size of animals found in the intertidal of Monte Tigre progressively increased from |$\sim 50 \ {\rm mm}$| CL in October to |$\sim 105$| and 75 mm CL in December for males and females, respectively (Fig. 4). The sex ratio increased from October to December; male : female ratio was 1:1 in October and November 1999 (null |${\rm H}_{0} \ 1:1$|; |$G_{{\rm w}} = 0.018$|; |$P = 0.89; \ G_{{\rm w}} = 0.082; \ P = 0.77$|, respectively), and 2:1 in December 1997 and 1999 (null |${\rm H}_{0} \ 2$|:1; |$G_{{\rm w}} = 1.27$|; |$P = 0.26; \ G_{{\rm w}} = 3.29; \ P = 0.07$|, respectively). All 557 sampled males were in intermolt: 16%, 83%, and 1% had carapace conditions scored as hard without epibionts, fouled, and heavily fouled, respectively. In October and November, all 127 of females were in intermolt: 73% and 17% had carapace conditions scored as hard without epibionts and fouled, respectively. In December 1997 and 1999, 54% of the females |$(n = 215)$| were in pre- or postmolt condition. In December 1997, the average size of exuviae |$(n = 35)$| was similar to that of females in premolt condition (|$n = 56$|; Student’s |$t$|-test, |$t = -1.40; \ P = 0.16$|).
Discussion
The presence of L. confundens in coastal waters off the southern Province of Santa Cruz and the Atlantic coast of Tierra del Fuego changes our previous perception of the distribution of Lithodes spp. in the southwestern Atlantic. Earlier studies reported a continuous distribution of L. santolla from the Beagle Channel (55°S) to 35°S (Fig. 1; Boschi et al., 1984; Nakamura et al., 1986; Macpherson, 1988; Vinuesa, 1991; Boschi et al., 1992; Boschi, 1997) because the taxonomy was still unclear. The presence of L. santolla in the Beagle Channel, Strait of Magellan, and Golfo San Jorge is well known, because of fisheries and after Macpherson’s (1988) review. However, exact ranges of distribution of Lithodes spp. between 47° and 55°S are still unclear. Using data from a survey done in 1959 at 13–95 m depth (Angelescu, 1960), we calculated that the abundance of L. confundens correlated negatively with depth |$(r = -0.38; \ P \lt 0.01)$|. The abundance of L. confundens apparently reaches its maximum near Río Gallegos and Río Grande. From Angelescu’s (1960) data, we calculated that the maximum density of L. confundens of 2.3 crab·m tangle |${\rm net}^{-1}$| occurred at 51°20′S, at the latitude of Monte Tigre, and decreased northerly and southerly. A second peak of |$0.6 \ {\rm crab} \cdot {\rm net \ m}^{-1}$| was detected off Tierra del Fuego, at 53°20′S. This value coincides with maximum captures of |$1.5 \ {\rm crab} \cdot {\rm trap}^{-1}$| at 53°50′S, recorded in 1986 off Río Grande, by the survey of the FV Hoshin Maru II (Boschi, 1997). Crabs from this survey were reported to be L. santolla, but no carcinologist certified their identity (E. E. Boschi, Instituto Nacional de Investigación y Desarrollo Pesquero — INIDEP, Mar del Plata, Argentina, personal communication). However, because peaks of abundance and average sizes of males and females were coincident with previous studies (Angelescu, 1960; Scelzo, 1974) and with our own (Table 2), we suspect that crabs captured by the FV Hoshin Maru II were L. confundens. Lithodes santolla has never been found in the intertidal where L. confundens is abundant, although in the Beagle Channel, the former species may occur at depths as low as 0.5 m (personal observations). Furthermore, if L. santolla occurred in other beaches, as for example in Golfo San Jorge, its occurrence would have been reported. Surveys done by Angelescu (1960) and the INIDEP in recent years (G. Wyngaard, INIDEP, Mar del Plata, Argentina, personal communication) support that no Lithodid crabs occur off the Atlantic coast of Argentina between 47° and 49°S. The only evidence supporting the presence of L. santolla between 47°S and 55°S is only one specimen collected at |$\sim 51^\circ {\rm S}, \ 57^\circ {\rm W}$|, on the continental slope at 255–352 m depth (Macpherson, 1988), but comprehensive samplings are still needed. Therefore, we speculate that in Atlantic waters between Puert San Julián and Cabo San Pablo (49°15′–54°30′S), L. confundens occurs on coastal shallows, and L. santolla is restricted to deeper waters.
Source . | Geographical range . | |$\hbox{Tangle nets yield }(\pm {\rm SD})$| . | Other method . | |$\hbox{Average size }(\pm {\rm SD})$| in mm CL Female Male . |
---|---|---|---|---|
This study | 51°21′S, 69°02′W | |$0.24 \ (\pm 0.15) \ {\rm crabs} \cdot {\rm m}^{-1}$| tide (~ 0.48 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | |$74.2 \,(\pm 12.3)$|(1)/|$75.1 \,(\pm 8.2)$|(2) | |
|$107.5 \,(\pm 17.4)$|(1)/|$101.3 \,(\pm 13.4)$|(2) | ||||
Scelzo (1974) | 51°21′S, 69°02′W | 0.04–0.09 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 80.3 | |
118.9 | ||||
Angelescu (1960) | 49°–54°15′S | |$0.46 \,(\pm 0.90)$| males |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 42.8 males |$\cdot{\rm h}^{-1}$| (trawl net) | – |
123.7(3) (~ 115 mm CL) | ||||
Boschi (1997) (FV Shinmei—1972)(4,5) | 50°55′–52°20′S | 0.13–0.21 kg |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| (~ crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | ||
Bosch (1997) (FV Hoshin—1986)(4,5) | 51°44′–54°43′S | |$0.17 \,(\pm 0.32)$| males |$\cdot{\rm trap}^{-1}$| | |$72.5 \pm 6.8$|(6) | |
|$116.3 \pm 9.3$| |
Source . | Geographical range . | |$\hbox{Tangle nets yield }(\pm {\rm SD})$| . | Other method . | |$\hbox{Average size }(\pm {\rm SD})$| in mm CL Female Male . |
---|---|---|---|---|
This study | 51°21′S, 69°02′W | |$0.24 \ (\pm 0.15) \ {\rm crabs} \cdot {\rm m}^{-1}$| tide (~ 0.48 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | |$74.2 \,(\pm 12.3)$|(1)/|$75.1 \,(\pm 8.2)$|(2) | |
|$107.5 \,(\pm 17.4)$|(1)/|$101.3 \,(\pm 13.4)$|(2) | ||||
Scelzo (1974) | 51°21′S, 69°02′W | 0.04–0.09 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 80.3 | |
118.9 | ||||
Angelescu (1960) | 49°–54°15′S | |$0.46 \,(\pm 0.90)$| males |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 42.8 males |$\cdot{\rm h}^{-1}$| (trawl net) | – |
123.7(3) (~ 115 mm CL) | ||||
Boschi (1997) (FV Shinmei—1972)(4,5) | 50°55′–52°20′S | 0.13–0.21 kg |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| (~ crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | ||
Bosch (1997) (FV Hoshin—1986)(4,5) | 51°44′–54°43′S | |$0.17 \,(\pm 0.32)$| males |$\cdot{\rm trap}^{-1}$| | |$72.5 \pm 6.8$|(6) | |
|$116.3 \pm 9.3$| |
1997;
1999;
Reported only male carapace width.
The name of the fishing vessel and year of survey is indicated between parentheses.
Reported as L. santolla, but see text.
Data from off Tierra del Fuego at 53°50′S, 67°19′W.
Source . | Geographical range . | |$\hbox{Tangle nets yield }(\pm {\rm SD})$| . | Other method . | |$\hbox{Average size }(\pm {\rm SD})$| in mm CL Female Male . |
---|---|---|---|---|
This study | 51°21′S, 69°02′W | |$0.24 \ (\pm 0.15) \ {\rm crabs} \cdot {\rm m}^{-1}$| tide (~ 0.48 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | |$74.2 \,(\pm 12.3)$|(1)/|$75.1 \,(\pm 8.2)$|(2) | |
|$107.5 \,(\pm 17.4)$|(1)/|$101.3 \,(\pm 13.4)$|(2) | ||||
Scelzo (1974) | 51°21′S, 69°02′W | 0.04–0.09 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 80.3 | |
118.9 | ||||
Angelescu (1960) | 49°–54°15′S | |$0.46 \,(\pm 0.90)$| males |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 42.8 males |$\cdot{\rm h}^{-1}$| (trawl net) | – |
123.7(3) (~ 115 mm CL) | ||||
Boschi (1997) (FV Shinmei—1972)(4,5) | 50°55′–52°20′S | 0.13–0.21 kg |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| (~ crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | ||
Bosch (1997) (FV Hoshin—1986)(4,5) | 51°44′–54°43′S | |$0.17 \,(\pm 0.32)$| males |$\cdot{\rm trap}^{-1}$| | |$72.5 \pm 6.8$|(6) | |
|$116.3 \pm 9.3$| |
Source . | Geographical range . | |$\hbox{Tangle nets yield }(\pm {\rm SD})$| . | Other method . | |$\hbox{Average size }(\pm {\rm SD})$| in mm CL Female Male . |
---|---|---|---|---|
This study | 51°21′S, 69°02′W | |$0.24 \ (\pm 0.15) \ {\rm crabs} \cdot {\rm m}^{-1}$| tide (~ 0.48 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | |$74.2 \,(\pm 12.3)$|(1)/|$75.1 \,(\pm 8.2)$|(2) | |
|$107.5 \,(\pm 17.4)$|(1)/|$101.3 \,(\pm 13.4)$|(2) | ||||
Scelzo (1974) | 51°21′S, 69°02′W | 0.04–0.09 crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 80.3 | |
118.9 | ||||
Angelescu (1960) | 49°–54°15′S | |$0.46 \,(\pm 0.90)$| males |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| | 42.8 males |$\cdot{\rm h}^{-1}$| (trawl net) | – |
123.7(3) (~ 115 mm CL) | ||||
Boschi (1997) (FV Shinmei—1972)(4,5) | 50°55′–52°20′S | 0.13–0.21 kg |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$| (~ crabs |$\cdot{\rm m}^{-1}$||$\cdot{\rm d}^{-1}$|) | ||
Bosch (1997) (FV Hoshin—1986)(4,5) | 51°44′–54°43′S | |$0.17 \,(\pm 0.32)$| males |$\cdot{\rm trap}^{-1}$| | |$72.5 \pm 6.8$|(6) | |
|$116.3 \pm 9.3$| |
1997;
1999;
Reported only male carapace width.
The name of the fishing vessel and year of survey is indicated between parentheses.
Reported as L. santolla, but see text.
Data from off Tierra del Fuego at 53°50′S, 67°19′W.
Lithodes confundens occurs in the intertidal between October and January. The only evidence of molting crabs was for females in December, and that was coincident with mating. Moreover, the average size of exuviae was similar to that of molting females. Crabs that occurred first in the intertidal were smaller than crabs that occurred in December (Fig. 4). We reject the possibility that small crabs molt in October and November and reach sizes found in December. In the Beagle Channel, L. santolla needs four molt stages and at least two years to grow from |$\sim 50$| to 75 mm CL (Vinuesa et al., 1990). Hence, it is unlikely that L. confundens has such an extremely different growth rate.
In December, our finding of mating pairs in the intertidal is coincident to what occurs in other lithodid species. Couples of L. santolla and Paralomis granulosa at the Beagle Channel occur sheltered within the kelp forest at less than 10 m depth (Lovrich et al., 2002, and personal observations). The occurrence in shallow waters of Paralithodes camtschaticus has also been associated with life-history events, mainly molting (Wallace et al., 1949) and mating (Powell and Nickerson, 1965; Powell et al., 1974). Previous studies also reported that L. confundens was concentrated near the coastline during summer (Angelescu, 1960; Scelzo, 1974; Boschi, 1997), in shallow waters during spring and autumn (Boschi, 1997), and hence suggested a vertical migration. However, in contrast to southern lithodids, in the Bering Sea female and juvenile P. camtschaticus display an aggregated distribution in shallow waters during winter. Spatial and temporal variations in temperature, salinity, and photoperiod trigger vertical movements in P. camtschaticus (Dew, 1990; Stone et al., 1992). Lithodids of the southwestern Atlantic have the same environmental cues as those in the northern Bering sea: temperature ranges between 4.5° and 9.5°C, salinity 29–32 ppt, and photoperiod 8–18 h. However, southern crabs seem to occur in shallow waters in summer rather than in winter.
Results of surveys for lithodids off southern South America are summarized in Table 2. From tangle nets, catch per unit effort (CPUE) has varied throughout the different years of sampling. Our value of |$0.48 \ {\rm crabs} \cdot {\rm m \ net}^{-1} \cdot {\rm d}^{-1}$| is within the same order of magnitude of previous abundance estimations performed off Santa Cruz and Tierra del Fuego (cf. Angelescu, 1960; Boschi, 1997), yet CPUEs for the intertidal fishery at Monte Tigre in summers 1971–1973 were considerably lower (cf. Scelzo, 1974). The size structure of the population of L. confundens seems to be consistent through the time because our estimations of average sizes of female and male fractions of the population are similar to those previously reported (Table 2). Nevertheless, a precise stock assessment of the population of L. confundens should precede any commercial exploitation.
Sexual maturity is important information for king crab fisheries managed by means of a legal size limit. The rationale of the minimum harvest size is that such a size would preserve sufficient males for breeding. In the Beagle Channel, the fishery for Lithodes santolla has a legal size of 110 mm CL (Lovrich, 1997). Hence, male crabs are allowed to mate at least once before they recruit into the fishery because functional or behavioral maturity is attained at 94.4 mm CL. The change of relative growth of the male right chela occurs at 75.4 mm CL, one or two instars previous to the functional maturity (Lovrich et al., 2002). In contrast, male L. confundens seemingly attains functional maturity at |$\sim 85 \ {\rm mm \ CL}$| (Fig. 3A), probably at the same molt stage at which the change in chela allometry occurs, i.e., 87.3–89.8 mm CL (Table 1). In the Beagle Channel, the legal size for L. santolla is 15% larger than the functional maturity, i.e., 94.4 mm CL. Other exploratory fisheries have set minimum size limits as 10% greater than the size at maturity (Otto and MacIntosh, 1996). Therefore, from data presented in this study, we consider that a legal size of 15% greater than the estimated functional maturity of L. confundens could be adequate for any fishery off Santa Cruz and Tierra del Fuego. Hence, the suggested legal size is 100 mm CL.
The present board of data is important for fishery management in the future. First, we determined that sporadic fisheries near Río Gallegos and Río Grande have removed L. confundens in lieu of L. santolla. Second, the development of these fisheries for L. confundens is expected mainly because the fishery for L. santolla in the Beagle Channel collapsed and closed in 1994 (Lovrich, 1997) and still remains closed. In the Golfo San Jorge, L. santolla is fished by trawling. This has a high impact on the population because there is neither sex nor size selectivity nor returns to the sea of sublegal crabs (Vinuesa et al., 1998). Hence, the fishery mortality is supposedly high enough to significantly reduce the size of the population. If the abundance of L. confundens is commercially acceptable, the reallocation of the fishing effort on king crabs could be expected, and biological information is needed for a more sustainable fishery management in the future.
Acknowledgments
The Centro Austral de Investigaciones Científicas and the Subsecretaría de Pesca y Actividades Portuarias of the Argentine Province of Santa Cruz provided institutional support. We thank Sven Thatje, Enrique Boschi, and three anonymous reviewers for comments on the manuscript that helped its improvement. This study was funded by grants of the International Foundation for Science (Stockholm, Sweden — grant A-2507/1) and by the Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 4307/97). The Government of the Province of Santa Cruz (Disp. SEP 125/01) partially funded the page charges of the present article.