110 



Fishery Bulletin 102(1) 



ing periods of chinook and coho salmon, and steelhead trout 

 also occur during these times. 



During fall 1997, all harbor seal scats present at the 

 haulouts were collected every other day during the day- 

 time low tide, weather permitting (Table 1). In 1998. bi- 

 weekly attempts were made to pick a minimum of 50 scats 

 during low tides at the haulout sites (Table 1). Scats were 

 collected, placed in individual plastic bags, and frozen for 

 later processing. At the laboratory samples were thawed 

 and rinsed in nested sieves (1.0 mm, 0.71 mm, and 0.5 mm 

 in 1997; 1.4 mm, 1.0 mm, and 0.5 mm in 1998). Fish struc- 

 tures were dried and stored in glass vials and cephalopod 

 remains were stored in vials with 70"* isopropyl or ethyl 

 alcohol. 



Prey were identified to the lowest possible taxon by using 

 sagittal otoliths, skeletal, and cartilaginous remains from 

 fish and beaks and statoliths from cephalopods. Other in- 

 vertebrate remains were discarded from analysis because 

 of the uncertainty of identifying them as primary or sec- 

 ondary prey. Unknown prey were categorized as "unidenti- 

 fied" and "unidentifiable" (Browne et al., 2002). Items that 

 were categorized as "unidentifiable" were excluded from 

 analyses because they could not be distinguished from 

 prey already identified in the sample. Otoliths, beaks, and 

 diagnostic bones were identified by using an extensive ref- 

 erence collection at the NMML and voucher samples veri- 

 fied by Pacific Identifications (Victoria, British Columbia). 



After identification, otoliths were separated by side (left, 

 right, or unknown ) and enumerated to determine minimum 

 number of specific prey. Unique diagnostic structures (e.g. 

 quadrates, angulars, basioccipitals, vomers) were used for 

 identification and enumeration offish. Non-unique skeletal 

 structures such as gillrakers and teeth were used to iden- 

 tify but not enumerate taxa (i.e. their presence indicated 

 only a single individual) unless the structures were from 

 different size classes. Vertebrae were treated like other 

 non-unique structures; however, for salmon, if the number 

 of vertebrae reflected more than one individual, then they 

 were used for enumeration. Cephalopod beaks were sepa- 

 rated by side (upper, lower, or unknown) and enumerated 

 to determine number of prey. 



To discern where harbor seals were feeding, identified 

 prey were categorized as those exclusively found in rivers 

 or estuaries (e.g. gobiids, cyprinids), those found exclu- 

 sively in marine waters (e.g. gadids, mvxinids), and those 

 that could potentially be found in either environment (e.g. 

 anadromous species, osmerids, petromyzontids) by using 

 Eschmeyer et al. (1983). A seal was considered to feed in 

 the river-estuary system if all the prey taxa identified in 

 the scat were definitely or could potentially be found in the 

 system. For example, a sample containing remains of pea- 

 mouth chub iMylocheilus caurinus), threespine stickleback 

 ( Gasterosteus aculeatus ), river lamprey iLampetra ayresii ), 

 and chinook salmon would be classified as a riverine- 



