Distribution Pattern, Age, and Growth of Blue Sharks in the South Atlantic Ocean

Figures & data

FIGURE 1. Fishing effort and Blue Shark (BSH) size (FL, cm) recorded by Taiwanese observers on longline fishing vessels operating in the South Atlantic from 2004 to 2013. The color scale within grid cells represents fishing effort, with darker blue representing more hooks and lighter blue representing fewer hooks. The size of the red dots indicates the mean FL categorized using 25th percentiles of the data.

TABLE 1. Sample sizes and TL ranges of Blue Shark specimens that were captured from the South Atlantic (2006–2011) and used for age analyses.

	Females		Males		Sex unknown
Month	n	TL (cm)	n	TL (cm)	n	TL (cm)	Total n
Jan	35	168–247	13	167–291	5	199–265	53
Feb	15	177–255	18	167–289	32	171–292	65
Mar	29	162–260	22	175–269	11	175–282	62
Apr	28	181–265	45	161–265	18	181–255	91
May	37	150–280	51	152–286	22	191–288	110
Jun	38	180–279	53	139–295	15	196–283	106
Jul	13	169–293	29	164–310	13	205–325	55
Aug	7	190–260	15	158–310	5	211–320	27
Sep	9	190–250	28	180–282	4	210–260	41
Oct	8	202–254	16	210–272	4	210–261	28
Nov	4	245–276	6	215–262	4	218–276	14
Dec	88	100–323	39	110–270	4	228–275	131
Total	311	100–323	337	110–310	137	171–325	785

FIGURE 2. An example X-ray image of a Blue Shark vertebral centrum (from a female, 205 cm TL) magnified by Adobe Photoshop CS4 version 11.0 and displayed on screen. The number of growth band pairs is depicted; R = the radius.

FIGURE 3. Length frequency distribution (FL, cm) of Blue Shark specimens captured by Taiwanese longline fleets in two areas of the South Atlantic: (a) the equatorial–tropical area and (b) the subtropical–temperate area (black bars = males; open bars = females; hatched bars = individuals of unknown sex).

FIGURE 4. Length frequency distribution (TL, cm) of Blue Shark specimens that were used for age and growth analyses in this study (black bars = males; open bars = females; hatched bars = individuals of unknown sex).

FIGURE 5. Seasonal fishing effort and Blue Shark (BSH) size (FL, cm) recorded by Taiwanese observers on longline fishing vessels operating in the South Atlantic from 2004 to 2013 (seasons are defined in Methods). The color scale within grid cells represents fishing effort, with darker blue representing more hooks and lighter blue representing fewer hooks. The size of the red dots indicates the mean FL categorized using 25th percentiles of the data.

FIGURE 6. Annual mean (±SD) catch at size (FL, cm) for Blue Sharks captured by Taiwanese longline fleets operating in two areas of the South Atlantic from 2004 to 2013: (a) the equatorial–tropical area and (b) the subtropical–temperate area (the number above [females] or below [males] each data point is the sample size).

FIGURE 7. Age bias plot of vertebral band pair counts for Blue Sharks captured by Taiwanese longline fleets in the South Atlantic (black circles = mean [±2 SE] counts by reader 1 relative to reader 2; the number above each data point is the sample size).

TABLE 2. Comparison of von Bertalanffy growth function parameters for Blue Sharks examined in the present study and previous studies (L_∞ = asymptotic length; k = Brody growth coefficient; t₀ = theoretical age at zero length; t_max = maximum observed age).

Study area	Sex	N	L∞ (TL, cm)	k	t0	tmax	Reference
Eastern South Atlantic	Combined	742	352.1	0.13	–1.31	15	Present study
North Atlantic	Combined		394.0	0.133	–0.80		Aasen 1966
	Combined	82	423.0	0.11	–1.04	6	Stevens 1975
	Male	287	337.6	0.18	–1.35	16	Skomal and Natanson 2003
	Female	119	371.2	0.13	–1.77	15
	Combined	411	343.6	0.17	–1.43	16
Northeast Atlantic	Combined	159	376.5	0.12	–1.33		Henderson et al. 2001
Western South Atlantic	Combined	236	352.0	0.16	–1.01	12	Lessa et al. 2004
Eastern North Pacific	Male	38	295.3	0.18	–1.11	9	Cailliet et al. 1983
	Female	88	241.9	0.25	–0.80	9
Western North Pacific	Male	43	369.0	0.10	–1.38	7	Tanaka et al. 1990
	Female	152	304.0	0.16	–1.01	8
	Male	181	375.8	0.12	–1.55	14	Hsu et al., working paper, 2011
	Female	250	317.4	0.17	–1.12	12
North Pacific	Male	148	378.8	0.13	–0.76	10	Nakano 1994
	Female	123	318.5	0.14	–0.85	10
Western South Pacific	Male	593	299.9	0.10	–2.44	16	Blanco-Parra et al. 2008
	Female	324	237.5	0.15	–2.15	12
Central South Pacific	Male	164	366.9	0.13	–1.33	14	Hsu et al., working paper, 2012
	Female	81	348.0	0.16	–1.01	11

FIGURE 8. Results of centrum edge analysis of vertebral centra from Blue Sharks captured by Taiwanese longline fleets in the eastern South Atlantic (black bars = translucent bands; open bars = opaque bands; the number above each bar is the combined-sexes sample size).

FIGURE 9. The von Bertalanffy growth function (VBGF) fitted to observed TL-at-age data for Blue Sharks captured by Taiwanese longline fleets in the eastern South Atlantic (open circles = males; open triangles = females; ×-symbols = individuals of unknown sex; solid line = VBGF for both sexes combined).

FIGURE 10. Comparison of growth curves (TL at age) for Blue Sharks (M = males; F = females) sampled in the Atlantic Ocean during the present study and in previous studies (Stevens 1975; Henderson et al. 2001; Skomal and Natanson 2003; Lessa et al. 2004).

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