-64- 



farthest south, chinstrap penguins are somewhat inter- 

 mediate, and gentoo penguins are generally closer to the 

 Convergence (Sladen, 1964; Watson et al., 1971). There 

 are, however, large areas in which species overlap. While 

 both macaroni and rockhopper penguins breed together on a 

 few islands near the Convergence, macaroni penguins extend 

 their range to the South Shetland Islands while rockhopper 

 penguins do not. 



Carrick and Ingham (1967) related distribution patterns 

 of these species to nesting and feeding area availability, 

 and found some evidence suggesting that feeding areas are 

 especially critical. Emperor penguins have a theoretically 

 unlimited supply of fast ice to breed on, yet colonies re- 

 main in traditional areas (presumably) near adequate fishing 

 grounds (Carrick and Ingham, 1967) . The relationship of 

 food resources and penguin distribution is also illustrated 

 by the pattern of chinstrap marked range expansion within 

 the past 20 years. This pattern may have resulted from re- 

 duced competition for food following zonal depletion of 

 whale stocks (Sladen, 1964; Conroy, 1975). 



b. Movements and Stock Identification 



With the possible exception of gentoo penguins, there 

 are no data to reject the idea that most of these species, 

 either as immatures or seasonally as adults, move considerable 

 distances on a regular basis. Both adelie and chinstrap 

 penguins generally associate with the pack ice in winter, 

 and chinstrap penguins are found in pelagic habitats con- 

 siderable distances from known breeding areas (Routh, 1949; 

 Szijj, 1967; Fraser, pers. comm.). In contrast, a well 

 marked size dimorphism existing between northern and 

 southern populations of gentoo penguins suggests limited 

 movement and gene flow between these two areas (Watson et al., 

 1971) . A similar dimorphism exists among other island- 

 breeding species such as rockhopper penguins — thorough pres- 

 ent information is inadequate to confirm if these populations 

 may be considered demes. 



c. Standing Stock 



Data on either the biomass or standing stock of penguins 

 are not easily acquired (Falla, 1964; Laws, 1977b). This 

 difficulty is reflected in the ranges of estimates (Table 12). 

 It is agreed that penguins are the most important avian 

 Antarctic group and account for 88% to 91% of total avian 

 biomass (Croxall, unpub, MS.; Prevost, 1978). If these 

 estimates are reasonably accurate, a biomass between 418 and 

 461 thousand metric tons of feeding penguins must certainly 

 have an important impact on zooplankton levels. 



