McBride et al.: Interspecific comparisons of searobin, Prionotus spp., movements, size structure and abundance 
307 
Sound 
Rhode Island Sound 
May 1 992 
Cape Ann 
Massachusetts Bay 
Cape Cod Bay 
Cape Cod 
Figure 3 
Geographic distribution of northern searobins (open symbols) and striped 
searobins (filled symbols) during two consecutive sampling seasons for the 
Massachusetts coastal survey (Table 2). The dotted line represents the off- 
shore limit of sampling (55 m). 
curred annually on parts of Georges Bank and in the 
southern portion of the Gulf of Maine during sum- 
mer and autumn. In general, both species were 
broadly distributed within the central Mid-Atlantic 
Bight but moved southward during winter and spring 
(Figs. 2 and 4). Striped searobins moved well south 
and west of Hudson Canyon, which appears as an 
approximate northern limit for striped searobins 
during the overwintering season, whereas northern 
searobins had a broader latitudinal distribution in 
the Mid-Atlantic Bight while overwintering (see also 
McBride and Able, 1994). These data suggest that 
by spring large striped searobins moved either far- 
ther offshore into continental slope waters (>200 m) 
or migrated south of the zoogeographic boundary 
represented by Cape Hatteras (i.e. between the Mid- 
Atlantic and the South Atlantic Bight) because sizes 
> 25 cm TL are uncommon during spring cruises (Fig. 
5). We cannot prove this hypothesis, however, because 
these southern and offshore regions were not well 
sampled during the overwintering season (see Table 2 
for sampling area limits). 
Both searobin species migrated seasonally in an 
onshore-offshore direction as well as in a north- 
south direction (Fig. 2). Northern searobins were, 
however, consistently found in significantly deeper 
waters than were striped searobins during both 
spring (78.3 m ± 5.27 vs. 60.4 m ± 9.30; mean depth 
± 95% confidence limits [CL] ) and autumn (30.7 m ± 
1.73 vs. 20.0 m ± 1.44) during 1982-91. Northern 
searobins were also found in significantly colder bot- 
tom temperatures than were striped searobins in 
spring (9.2 ± 0.3°C vs. 11.8 ± 0.56°C; mean ± 95% 
CL) and autumn (17.6 ± 0.40°C vs. 19.6 ± 0.40°C), 
although both species were collected in a wide range 
of temperatures (4-28°C) during 1982-91. These re- 
sults support McBride and Abie’s (1994) postulation 
that temperature is the principal factor producing 
distinctive geographic distributions for each species. 
Other western North Atlantic searobins (Prionotus 
and Bellator species) that are distributed in subtropi- 
cal and tropical waters reside within species-specific 
depth regions but show little tendency to migrate 
seasonally (Lewis and Yerger, 1976; Ross, 1977; 
Floyd, 1980; Hoff, 1992). South of Cape Hatteras, 
where temperatures fluctuate less between seasons 
than in the Mid-Atlantic Bight, even northern 
searobins show little tendency to migrate seasonally 
(Floyd, 1980). 
Size structure 
Modal size of northern searobins was consistent be- 
tween seasons (17-21 cm TL), but striped searobins 
were both larger and more variable in size ( 18-28 
cm TL; Fig. 5). The larger size ofP. evolans is largely 
accounted for by its faster growth rate and greater 
maximum age (Richards et al., 1979). An earlier 
analysis of NMFS survey data has reported north- 
ern searobins as large as 34 cm and striped searobins 
as large as 41 cm (Wilk et al., 1978). The maxima 
observed in our study were 5-7 cm larger, but these 
