Winter foraging behaviour of lactating New Zealand sea lions (Phocarctos hookeri)

Figures & data

Figure 1  Auckland Islands showing the main breeding islands for NZ sea lions: Enderby, Dundas and Figure of Eight. Inset: New Zealand's sub-Antarctic area.

Figure 2  Frequency distribution of mean percentage of dives in each depth category for eight female NZ sea lions, winter foraging.

Figure 3  Kernel range of all filtered satellite locations for lactating NZ sea lions from: A, Enderby Island, July to September 1996–1997 (n=6) and B, Enderby Island, January and February 2001–2004 (n = 26). Intensity of shading of kernel ranges represents percentage of time spent in the area displayed as highest concentration of locations (darkest) to lowest concentration (lightest). Bathymetric contours are shown as thin black lines, with the Auckland Islands shelf represented by the 500 m bathymetric boundary. Arrow squid Nototodarus sloanii trawl fishery effort (50% and 95% kernel ranges) from: A, January to April 1996–1997 and B, February to April 2001–2007 are represented by thick black solid lines. Scampi Metanephrops challengeri trawl fishery effort (50% and 95% kernel ranges): A, all year 1996–1997 and B, all year 2001–2007 are represented by dashed black lines. A, all other trawl fisheries activities (50% and 95% kernel ranges), all year 1996–1997 are represented by dotted black lines.

Table 1  Summary of statistics from the diving records of eight female NZ sea lions while at sea during the austral winters 1996 and 1997. Dives are defined as submersions > 6 m. All means presented±SE.

Female identity	Year	No. trips	No. dives	Mean dives per foraging cycle	Mean dives per hour at sea	Mean dive depth (m)			Mean dive duration (min)			% bottom time
						Mean	SE	Max	Mean	SED	Max
E30	1996	13	5233	436	5.2	140	0.6	294	5	0.2	8.3	56
E31	1996	6	2470	494	4.9	90	0.9	170	4	0.3	8.3	55
E32	1996	7	4013	669	6.9	122	1.0	434	4.5	0.3	10.2	60
E33	1996	9	6520	815	6.5	119	0.8	314	4.5	0.3	9.8	58
E34	1996	10	6717	746	7.6	88	0.6	210	3.6	0.2	8.4	58
E80	1997	12	8909	742	7.1	122	0.4	256	5.3	0.2	9.4	64
E82	1997	15	6900	460	6.1	142	0.7	340	5.1	0.2	9.8	57
E83	1997	3	2524	841	6.6	122	1.4	412	4.4	0.4	10.0	52
Winter mean					6.4±0.3	118±0.8			4.6±0.3			60±1.3
Summer mean 1995^1 (n=14)					7.5±0.7	125±9.0			3.8±0.1			46±3.4
Summer mean 1997^2 (n=12)					8.1±0.7	124±10.4			3.4±0.2			38±1.6
Summer mean 2003–04^3 (n=18)					7.8±0.3	129±5.4			3.9±1.0			40±2.9
Summer (benthic) mean 2003–04^4 (n=10)					8.2±0.4	121±8.0			4.2±0.1			50±2.1
Summer (meso) mean 2003–04^4 (n=8)					7.3±0.3	140±4.8			3.7±0.1			28±0.4
Notes: ^1Gales & Mattlin 1997; ^2Costa & Gales 2000; ^3Chilvers et al. 2006; ^4Chilvers & Wilkinson 2009.

Table 2  Summary of foraging cycle and behaviour for eight female NZ sea lions tracked during winter 1996–97. Dives are defined as submersions > 6 m. Calculated aerobic dive limits (cADL) was estimated based on a useable oxygen store of 47.4 ml O₂ kg⁻¹ (Costa et al. 1998) and assuming a diving metabolic rate of 58.7 ml O₂ kg^−0.75 min⁻¹ (Costa & Gales 2000).

Female identity	Year	Mass at deployment (kg)	Mean time ashore (h)	Mean time at sea (h)	% time at sea per foraging cycle	% time submerged when at sea	cADL (min)	% dives exceed cADL
E30	1996	114.0	28.5	79.6	74	44	4.5	84
E31	1996	122.5	28.5	74.7	72	34	4.5	40
E32	1996	115.5	29.5	79.7	73	54	4.5	72
E33	1996	114.0	40.1	113.3	74	48	4.5	69
E34	1996	138.5	46	95.5	67	45	4.6	33
E80	1997	128.0	103.1	40.2	28	59	4.6	86
E82	1997	127.0	70.8	35.3	33	52	4.4	79
E83	1997	112.0	126.9	61.6	33	48	4.6	60
Winter mean		123±2.9	59.2±13.3	72.5±9.3	57±7.5	48±2.6		65±6.9
Summer mean 1995^1		114±4.3			57±2.9	45±2.9		44±4.7
Summer mean 2003–04^2		114±2.9	31.3±1.2	52.8±1.7	61±1.7	52±2.3		68±4.4
Summer (benthic) mean^3			35.7±2.7	62.6±5.0	64±1.4	57.5±3.1		82.1±2.5
Summer (mesopelagic) mean^3			33.5±4.2	45.5±5.1	58±3.1	46.6±2.1		51.2±2.5
Notes: ^1Gales & Mattlin 1997; ^2Chilvers et al. 2006; ^3Chilvers & Wilkinson 2009.

Table 3  Deployment year, number, durations of foraging trips and kernel range (KR) sizes for six NZ sea lions satellite tracked from Enderby Island (EI), Auckland Islands during the austral winters of 1996 and 1997. All means presented±SE.

Female identity	Year	No. days deployed	Total no. locations	Mean trip distance (km)	Max. trip distance (km)	Max. distance from EI	50% KR (km^2)	65% KR (km^2)	Mean distance from EI to centre KR (km)^1
E30	1996	39	234	275±11.8	326	126	281	670	109
E31	1996	48	146	207±15.6	266	106	722	1563	96
E32	1996	50	181	240±17.0	312	123	554	1115	109
E80	1997	41	91	242±16.2	307	128	430	919	122
E82	1997	53	178	189±7.5	236	102	539	815	91
E83	1997	58	263	324±30.6	419	136	420	681	123
Winter mean				246±19.7		120±5.4	491±61.2	960±138.1	108±5.3
Summer mean 2001–04^2				423±43.9		102±7.7	378±80.5	643±131.1	64±6.5
Summer (benthic) mean 2003–04^3				401±61.1		122±11.6	362±176	622±268.5	73.5±11.4
Summer (mesopelagic) mean 2003–04^3				531±111.7		98±13.8	130±24.5	234±45.2	57.2±16.3
Notes: ^1Mean straight line distance from KR to colony taken from the middle of both the KRs as they are both centred on the same area; ^2Chilvers et al. 2005; ^3Chilvers & Wilkinson 2009.

Costa , DP , Gales , NJ and Crocker , DE . 1998 . Blood volume and diving ability of the New Zealand sea lions, Phocarctos hookeri . Physiological Zoology , 71 : 208 – 213 .

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Costa , DP and Gales , NJ . 2000 . Foraging energetic and diving behaviour of lactating New Zealand sea lions, Phocarctos hookeri . Journal of Experimental Biology , 203 : 3655 – 3665 .

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