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Harbour porpoise (Northwest Atlantic population) COSEWIC assessment and status report: chapter 8

Habitat

Habitat requirements

The habitat requirements of harbour porpoises were reviewed by Gaskin (1992). Harbour porpoises occur primarily over continental shelves, although individuals are occasionally found in deeper waters (Read and Westgate 1997; Waring et al. 2001). The species, true to its name, is sometimes found in bays and harbours, particularly during the summer. In the Bay of Fundy, harbour porpoises frequent areas in which physiographic features may help to concentrate prey and facilitate prey capture (Gaskin and Watson 1985; Watts and Gaskin 1985; Gaskin 1992). Porpoises are relatively small and have a limited ability to store energy (see below), so they must feed frequently and stay relatively close to prey patches. In the Bay of Fundy and Gulf of Maine, individual porpoises equipped with satellite transmitters used very large home ranges and moved rapidly between patches of suitable habitat separated by tens or even hundreds of kilometres (Read and Westgate 1997). Individual porpoises may use the same habitat in consecutive years (Watson 1976).

Trends

There are no quantitative estimates of trends in the extent of habitat for harbour porpoises in eastern Canada. Gaskin (1992) noted a decrease in the use of some inshore areas of the Bay of Fundy by harbour porpoises during the late 1970s. There are significant inter-annual changes in the distribution of this species in the Bay of Fundy and Gulf of Maine that confound attempts to document changes in patterns of habitat use or abundance. These changes appear to be related to the distribution and abundance of prey (Palka 1995b; Trippel et al. 1999).

 

Table 1 (Wang et al. [1996]). Summary of differences among 3 subpopulations in Canada, as reflected in genetics and contaminants studies.
Study Test NFLD vs GSL GSL vs GOM NFLD vs GOM Comparison with other subpopulations
Wang et al. (1996)   Genetic Distance as % Nucleotide Divergence Genetic Distance as % Nucleotide Divergence Genetic Distance as % Nucleotide Divergence  
both sexes 1 ns 0.01 ** 0.011 *** All 3 subpopulations differ completely from Eastern North Pacific
females   * *** ***  

 

Table 1 (Rosel et al. [1999a]) continued. Summary of differences among 3 subpopulations in Canada, as reflected in genetics and contaminants studies.
Study Test NFLD vs GSL GSL vs GOM NFLD vs GOM Overall α Comparison with other subpopulations
Rosel et al. (1999a)   Genetic Distance as Fst value Genetic Distance as Fst value Genetic Distance as Fst value    
both sexes 2 0.020 * 0.042 ** 0.095 ** *** All 3 differ from MAS, GSL and WG don't differ
males 2 0.051 ** ns 0.062 ** * All 3 differ from MAS, GSL and WG don't differ
females 2 ns 0.115 ** 0.131 ** *** GOM and WG don't differ

MAS and NFLD don’t differ (small female n for MAS)
both sexes 3 ns ns ns ns  

Note: Genetic distances showed same trend as above, but were not significantly different from each other.

 

Table 1 (Tolley et al. [2001]) continued. Summary of differences among 3 subpopulations in Canada, as reflected in genetics and contaminants studies.
Study Test NFLD vs GSL GSL vs GOM NFLD vs GOM Comparison with other subpopulations
Tolley et al. (2001)   Genetic Distance as Fst value Genetic Distance as Fst value Genetic Distance as Fst value  
both sexes 2 0.020 * 0.042 ** 0.091 *** All differ from Norway, only GOM differs from Iceland

GSL and WG don't differ

 

Table 1 (Westgate and Tolley [1999]) continued. Summary of differences among 3 subpopulations in Canada, as reflected in genetics and contaminants studies.
Study Test NFLD vs GSL GSL vs GOM NFLD vs GOM Overall α
Westgate and Tolley (1999)   Order of Concentrations Order of Concentrations Order of Concentrations  
males 4 NFLD<GSL GSL<GOM NFLD<GOM ***
males 5 NFLD<GSL ns NFLD<GOM ***
males 6 NFLD<GSL GSL<GOM NFLD<GOM ***
females 4 NFLD<GSL GSL<GOM NFLD<GOM ***
females 5 ns ns ns ns
females 6 ns ns NFLD<GOM *

Note: Concentrations in NFLD always lowest, and sometimes notably lower than in the other two subpopulations.

Abbreviations: NFLD = Newfoundland, GSL= Gulf of St. Lawrence, GOM = Gulf of Maine and Bay of Fundy, MAS = mid-Atlantic states, and WG = West Greenland. All differences tabulated are significant at a table-wide a=0.05 assuming 3 comparisons, with criticala= 0.017 for the strongest pairwise difference, 0.025 for the next difference, and 0.05 for the weakest. Significance levels for pairwise comparisons are marked as "ns" for a> 0.05, * for 0.05=>a>0.01, ** for 0.01=>a>0.001, and *** for a< 0.001. Comparisons within Canada


Test details

1
BOF n=72, GOM n=21, GSL n=47, NFLD n=48, Eastern North Pacific n=16
RFLP of mtDNA, Chi-square contingency test used to compare frequencies
2&3
BOF & GOM n=80, GSL n=40, NFLD n=42, WG n=50, MAS n=41
2
d-loop mtDNA sequencing, analysis of molecular variance (AMOVA) for comparisons
3
7 microsatellite loci, AMOVA
4
BOF n=86, GOM n=15, GSL n=58, NFLD n=29, Eastern North Pacific n=16
d-loop mtDNA sequencing, analysis of molecular variance (AMOVA) for comparisons
5,6,&7
BOF & GOM n=51 males, 50 females; GSL n=31 males, 27 females; NFLD n=42 18 males, 11 females
5
Sum of PCBs, analysis of covariance for each sex with age as a covariate
6
Sum of CHBs, analysis of covariance for each sex with age as a covariate
7
Sum of CHLORs, analysis of covariance for each sex with age as a covariate

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