KROUSE: DISTRIBUTION OF JONAH AND ROCK CRABS 



The total commercial and research catch of 954 

 Jonah crabs included only 27 i2.8'f ) individuals 

  90 mm. This might be related to gear selectivity, 

 but this explanation loses credibility given that 

 numerous rock crabs (equivalent catchability to 

 Jonah crab) from 40 to 60 mm CW have been 

 sampled previously with conventional and mod- 

 ified lobster traps (Krouse 1976). Moreover, the 

 fact that no Jonah crabs 67 mm CW were ob- 

 served while hand-collecting 2,426 rock crabs 

 (mean 23.9 mm CW) during a 3-vr intertidal study 

 (Krouse 1976) or hauling research gear over a 9-yr 

 period (juvenile rock crabs were frequently seen in 

 traps) is evidence that small Jonah crabs in Maine 

 waters, unlike juvenile rock crabs, inhabit deeper 

 water exclusively. In the Mid-Atlantic Bight, Car- 

 penter (1978) reported that Jonah crabs <30 mm 

 CW were most abundant in depths  150 m, while 

 Haefner (1976) found crabs =s40 mm CW to be 

 most numerous between 75 and 150 m. Both inves- 

 tigators noted that the maximum abundance of 

 the larger crabs ( >40 mm) occured in the 150-400 

 m strata. 



Distribution 



From July 1968 through 1974, 459 Jonah crabs 

 were captured in 7,055 trap hauls (0.07 crab/trap 

 haul) wdth research gear fished near Boothbay 

 Harbor (Table 1). Fluctuations in the catch in as- 

 sociation with temporal and spatial variations in 

 fishing effort were assessed by plotting mean 

 monthly values of catch in numbers per trap haul 

 (catch per unit of effort, CPUE) for each fishing 

 area (Figure 6). In areas with relatively high 

 CPUE (average >0.1), catches gradually in- 

 creased throughout the summer, peaked in the 

 fall, and then diminished rapidly. Because most 

 crabs in the research catch were at least two molt 

 increments larger than the lower size limit of the 

 gear's selectivity range, the seasonal rise in CPUE 



Jon Feb Mar Apr May June July Aug Sepr Oct Nov Dec 

 MONTH 



Figure 6. — Monthly catch per unit of effort values for Jonah crabs 

 collected at various stations in the Boothbay Harbor region, 1968- 

 74. Number of trap hauls are in parentheses. Catch per unit of 

 effort outliers are marked by arrows. 



may be explained by recruits migrating into the 

 fishing areas. Conversely, the decline in CPUE in 

 winter may be attributed to the effects of fishing 

 mortality as well as emigration. Jonah crabs have 

 been reported by Jeffries ( 1966) to move into the 

 warmer waters of Narragansett Bay, R.I., from 

 spring through fall, followed in winter by a move- 

 ment to deeper, relatively warmer waters as in- 

 shore water temperature declined. The closely re- 



TaBLE 1. — Trap catch-effort values of Jonah and rock crabs caught in research traps at various stations near Boothbay 



Harbor, Maine, 1968-74. 



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