Size at Maturity and Fecundity of Rock Crabs, Cancer Irroratus, from the Bay of Fundy and Southwestern Nova Scotia

Rock crabs, Cancer irroratus, were collected from lobster traps, trawls, and by divers in the Bay ofFundy and southwestern Nova Scotia, 1980-81. Estimates of maturity were similar using gonad examination, measurements of chela height, and abdominal width/carapace width ratios. The carapace width (CW) at which 50% of male and female rock crabs were mature was estimated to be 62 and 49 mm, whereas the onset of maturity was estimated to be 40 and 27 mm CW,respectively. Ovigerous females (range 41-100 mm CW) Were heavier than nonovigerous females and males of the same carapace width, and carried from 47,130 to 567,690 eggs per female. Rock crabs in the Bay of Fundy and southwestern Nova Scotia appear to mature at a larger size than rock crabs from more southern waters. The rock crab, Cancer irroratus Say, 1817, (Decapoda: Brachyura), is common along the Atlantic coast of North America from Labrador to South Carolina (Rathbun 1930; Squires 1966; Nations 1975). In Canadian waters, C. irroratus is generally found near the coast (depth <20 m) and is abundant in the southern Gulf of St. Lawrence (Caddy and Chandler 1976; Stasko 1976; Campbell 1979). At present, C. irroratus is underutilized due to high processing costs and limited market demand. Consequently, rock crabs are fished primarily as an incidental bycatch in the lobster fishery and, except in certain areas, are generally discarded or occasionally used as bait in lobster traps. Bigford (1979) summarized the numerous studies on the biology and ecology ofC. irroratus. Little information exists on the reproductive biology ofC. irroratus in its northern range, especially the Bay of Fundy and southwestern Nova Scotia (Krouse 1972, 1976, 1980; Scarratt and Lowe 1972; Elner and Stasko 1978; Elner and Elner 1980). Size at maturity and fecundity are important parameters in determining reproductive potential and for managing a crab fishery. Crabs can be considered mature when males can mate successfully (Hartnoll1969) and females are capable of extruding eggs. Although egg-bearing by female crabs is an obvious indication of functional maturity, depending on I Invertebrates and Marine Plants Division, Department of Fisheries and Oceans, Biological Station, St. Andrews, N.B. EOG 2Xo, Canada. 2 Invertebrates and Marine Plants Division, Department of Fisheries and Oceans, Biological Station, St. Andrews, N.B.; present address; P.O. Box 226, St. Andrews, N.B. EOG 2XO, Canada. Manuscript accepled October 1982. FISHERY BULLETIN: VOL. 81, NO.2, 198:1. the season and other factors, a proportion of mature females may be found without external eggs at any given period. Estimation of maturity in these nonovigerous females and males can be determined by internal examination of the gonads (physiological maturity) and/or measurement of external morphological secondary sexual characteristics (functional maturity). This paper reports on the physiological and functional maturity, fecundity, and weight relations of different size-groups ofC. irroratus males and females collected from the Bay of Fundy and southwestern Nova Scotia waters (Fig. 1).