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Exploring intraspecific life history patterns in sharks 



Jason M. Cope 



School of Aquatic and Fishery Sciences 



University of Washington 



1122 NE Boat St 



Seattle, Washington 98105 



E-mail address icopeo u Washington edu 



Marine ecosystems compose the major 

 source (85%) of world fisheries pro- 

 duction (Garcia and Newton, 1997). 

 Although only a few fish species tend 

 to dominate fishery catches (Jennings 

 et al., 2001), a large diversity of fishes 

 representing varied taxonomic levels, 

 ecological guilds, and life histories 

 is commonly taken. Recently, 66% of 

 global marine resources were deter- 

 mined to be either fully, heavily, or 

 over-exploited (Botsford et al., 1997). 

 Considering the current state of many 

 fisheries, the large diversity of spe- 

 cies taken globally, and the general 

 lack of resources to adequately assess 

 many stocks, it has become important 

 to develop shortcuts that may pro- 

 vide methods fisheries scientists can 

 use to determine which stocks are in 

 danger of overexploitation and which 

 recovery plans are appropriate when 

 biological data are limited (Stobutzki 

 et al., 2001). 



Applications of life history the- 

 ory have proven a potentially use- 

 ful means to accomplish such tasks 

 (Stearns, 1992; Reynolds et al., 2001). 

 Life history traits such as maxi- 

 mum size and age, maturity, mortal- 

 ity, and growth are correlated among 

 teleost fishes (Adams, 1980; Wine- 

 miller and Rose, 1992; Gunderson, 

 1997; Cortes, 2000) and the relation- 

 ships among such traits can be used 

 to infer some general life history pat- 

 terns. These general patterns reveal 

 that teleost fishes with higher maxi- 

 mum ages tend to be larger, mature 

 later, grow more slowly, and have 

 lower natural mortality rates (K-se- 

 lected species, Adams, 1980), where- 

 as teleost fishes with lower maximum 

 ages tend to show the opposite rela- 

 tionships (r-selected species, Adams, 

 1980). Correlations among traits may 

 also allow one to approximate dif- 



ficult to measure life history traits 

 from traits that are easier to mea- 

 sure and possibly anticipate response 

 to exploitation rates where life his- 

 tory data are limited (Jennings et 

 al., 1999). 



Applying these patterns to fisher- 

 ies trends reveals some consistent 

 and useful explanations. Jennings 

 et al. (1998) found that teleost fishes 

 from the northeast Atlantic that have 

 decreased in abundance are gener- 

 ally K-selected species. Jennings et 

 al. (1999) demonstrated that tropical 

 teleost fishes of greatest maximum 

 sizes were most vulnerable to exploi- 

 tation. And Rochet (2000) illustrated 

 the limitations of life history plas- 

 ticity to compensate for heavy fish- 

 ing pressure among four orders of 

 teleosts. 



Elasmobranchs, and particularly 

 sharks, have also shown life history 

 patterns similar to those of teleosts 

 (Cortes, 2000; Frisk et al., 2001). 

 Cortes (2000) offered three general 

 life history patterns for sharks; 1) 

 large litters, moderate to high lon- 

 gevity, large size, small offspring, 

 slow growth, 2) small litters, high 

 longevity, large size, large offspring, 

 slow growth and 3) small litters, low 

 longevity, small size, small offspring, 

 fast growth. Simplified applications 

 of the life history patterns have also 

 been applied to elasmobranch fisher- 

 ies. Smith et al. (1998) demonstrated 

 that larger, later-to-mature Pacific 

 shark species have lower rebound po- 

 tentials (i.e., abilities to recover from 

 fishing pressure), whereas Frisk et 

 al. (2001) showed a similar pattern 

 in sharks and rays in the north At- 

 lantic. These relationships have been 

 recommended as particularly useful 

 when managing data-poor elasmo- 

 branch species (Musick et al., 2000). 



As indicated by the above studies, 

 variation in life history traits and 

 patterns among shark species is well 

 established (Cortes, 2000) and such 

 relationships may be useful for the 

 management of these fishes, but it is 

 not known how these relationships 

 may change within a species. Specifi- 

 cally, if and how do intraspecific life 

 history traits of cosmopolitan species 

 vary in different areas of the world? 

 The spiny dogfish (Squalus acanth- 

 ias) provides an alluring preamble 

 to the topic: northeast Pacific spiny 

 dogfish have been aged to 80-i- years, 

 and females mature at around 35 

 years (Jones and Geen, 1977; Saun- 

 ders and McFarlane, 1993), whereas 

 spiny dogfish in the north Atlantic 

 obtain a maximum age of about 40 

 years, maturing at 12 years (Rago 

 et al. 1998). 



In the present study, I used gen- 

 eralized linear models (GLMs) to in- 

 vestigate whether spatial differences 

 in life history traits, such as those 

 seen in the spiny dogfish, reveal con- 

 sistent patterns when compared with 

 other spatially resolved life history 

 information from other shark species. 

 I then, as demonstration of potential 

 utility, applied these models to pre- 

 dict life history trait values for areas 

 lacking information for two species of 

 shark, spiny dogfish (S. acanthias) 

 and blue shark iPiionace glauca). 



Materials and methods 



Information for five life history traits 

 (age at maturity, longevity (maximum 

 age), mean fecundity, maximum size, 

 and size at maturity) from 17 shark 

 species in six families (Appendix, 

 Table 1) for seven general areas 

 (North Pacific (NP); North Atlantic 

 (NoA); Gulf of Mexico (GM); Indian 

 Ocean (I); Central Pacific (CP); South 

 Pacific (SP); South Atlantic (SA)) 

 was extracted from three primary 

 literature sources (Smith et al., 1998; 

 Cortes, 2000, 2002). Area distinc- 

 tions were based on those by Cortes 



Manuscript submitted 6 December 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



1.5 September 2005 by the Scientific Editor. 



Fish. Bull. 104:311-320 12006). 



