Relocation Experiment

Tag retention, determined as the time postrelease before the tag stopped moving for all subsequent relocations, was 17-51 days in 1996, but less than 24 h in 2003 due to different attachment methods. Thus, results in 2003 reflect very short-term movements, and do not necessarily indicate final choice of habitat. Immediately on release, octopuses either readily reoccupied their previous dens (1996, released where captured), sought nearby shelter under kelp if it was available (2003, shallow releases), or fled (2003, deep releases, no cover in vicinity). Two octopuses, possibly seeking shelter, approached divers immediately on release.

1996 2001 £002 2003 2004

Year

Fig. 20.5 Individuals per quadrat of select crab species in live prey surveys, demonstrating the increase in prey availability over the course of this study.

1996 2001 £002 2003 2004

Year

Fig. 20.5 Individuals per quadrat of select crab species in live prey surveys, demonstrating the increase in prey availability over the course of this study.

First Second Third Capture Release relocation relocation relocation

Fig. 20.6 Captured and released octopuses moved deeper and selected higher quality habitats during relocaton.

Capture Release First Second Third relocation relocation relocation

Fig. 20.6 Captured and released octopuses moved deeper and selected higher quality habitats during relocaton.

All octopuses moved deeper by 2-40 m following release (Table 20.4), although not all remained deeper at their final relocation. The 1996 controls (released where captured) moved 3-13 m deeper, and subsequently returned to shallow water (<3 m). Two moved within hours of release; the third (Petunia) remained in her release location for three days before briefly moving deeper and then returning to her intertidal capture location. Habitat quality indices (without prey, HQI4s) for the 1996 releases did not increase above capture/release sites as the octopuses moved (Table 20.4). The 2003 controls (relocated shallow) each moved deeper by <4 m; while the 2003 treatment (relocated deep) each moved deeper by >10 m (Fig. 20.6, top). However, Gavin (relocated shallow) was released in a location where substantially deeper water was not directly accessible. While the distance that the octopuses moved was not correlated with the time postrelease until tag loss, Alan (relocated shallow) moved least and was released into the highest HQI, suggesting a link between movement and

Table 20.4 Octopuses in the relocation experiment. Depths relative to mean lower low water.

Capture

Release

Final

Final

Lowest

Weight

depth

depth

relocation

Capture

Release

Relocation

relocation

Octopus

(kg)

Sex

(m)

(m)

depth (m)

HQI4

HQI4

HQI4

HQI4

Petunia1

6.3

F

+0.1

+0.1

-0.3

3.5

=capture

3.5

Beth1

7.1

F

-1.0

-1.0

-2.7

3.5

=capture

3.0

Suzi1

7.4

F

-1.0

-1.0

-2.7

3.5

=capture

3.0

Alan2

4.0

M

-1.3

-3.9

-7.0

3.8

4.0

4.0

=final3

Gavin2

5.3

M

-1.9

-5.5

-7.8

2.3

2.3

2.5

2.0

Abby2

7.6

F

-2.5

-16.9

-54.9

4.0

1.3

1.0

=final3

Janice2

5.1

F

-1.2

-16.7

-19.9

3.8

1.0

2.0

1.0

'1996 octopus, released at capture site (control for handling artifacts). Lowest HQIs at relocation sites not available as only release and final relocation sites were surveyed.

22003 octopus, relocated and released either shallow (<6 m, relocation control) or deep (>10 m, treatment). Total distance moved within the first 24 h postrelease was 22 m for Alan, and 297, 344, and 563 m respectively for Gavin, Abby, and Janice.

3Alan and Abby were only tracked to a single relocation site, that was thus the lowest, highest, and final relocation HQI.

'1996 octopus, released at capture site (control for handling artifacts). Lowest HQIs at relocation sites not available as only release and final relocation sites were surveyed.

22003 octopus, relocated and released either shallow (<6 m, relocation control) or deep (>10 m, treatment). Total distance moved within the first 24 h postrelease was 22 m for Alan, and 297, 344, and 563 m respectively for Gavin, Abby, and Janice.

3Alan and Abby were only tracked to a single relocation site, that was thus the lowest, highest, and final relocation HQI.

habitat quality. Indeed, Alan was the only octopus to be released in an area with HQIs greater than his capture location.

For relocated (2003) octopuses, mean postrelease change in habitat quality index was 0.64, with only one value (for Abby) being negative (Fig. 20.6, bottom). Due to small sample size, habitat quality was not significantly different between capture and release sites; between release and relocation sites; nor between release and final relocation sites (HQI5 paired sample t-test, release to capture: t = 1.919, df = 3, p = 0.076, n = 4; release to first relocation: t = 0.151, df = 3, p = 0.445, n = 4; release to final relocation: t = -1.305, df = 3, p = 0.142, n = 4).

Across all 128 transects conducted 1995—2004, those in habitats with HQF greater than or equal to 2.75 had significantly greater octopus density than those in habitats with lower HQI4s (Independent samples t-test: HQI > 2.75, N = 85, avg density = 1.0 octopus per 1,000 sq. m surveyed; HQI < 2.75, N = 41, avg density = 0.4 octopus/1,000 sq. m, t = 2.823, df = 121, p = 0.006, N = 2 transects dropped due to missing data; equal variances not assumed). Thus, there were significantly more octopuses on transects with higher habitat quality. HQI4 did not, however, correlate with midden contents, which as indicators of octopus foraging success might also be expected to indicate habitat quality. No relationships were apparent between HQI4 or octopus density and either a Shannon Index (SI) of prey diversity in midden piles, the number of items in a midden, or summed size of all items in a midden. While surprising, this lack of correlation would be consistent with time- or risk-minimizing, if risk-adverse octopuses invested more foraging effort in poor habitats and spent more time in shelter where habitats were richer.

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