**Differences between dive transects and habitats (Fig. 3)**

Orange roughy showed significant differences in disturbance responses (p<0.01; Fig. 3a) between two transects that crossed adjacent habitats at similar depths (812-879 m) during dive ME10 (Table 1) with the ROV Aglantha on the northern Mid-Atlantic Ridge, just south

Deep-Sea Fish Behavioral Responses to Underwater Vehicles:

No response Close distance Far distance Arriving disturbed

**OB22-1**

**a b**

**Codling Roundnose**

a. Differences only in locomotion behavior (Fig. 5)

rates. No significant differences in vertical positioning occurred.

b. Differences only in locomotion and vertical positioning (Fig. 6a)

Biscay habitat, whereas it did not occur on the ridge site.

Mériadzek Terrace, Bay of Biscay

movement than the codling.

(Fig. 6b)

**% of Activity**

**0**

transects.

**20**

**40**

**60**

**80**

**100**

Differences Among Vehicles, Habitats and Species 231

**% of Activity**

Fig. 4. Disturbance responses of (a) codling and roundnose grenadier during a manned submersible transect and (b) codling and false boarfish during a ROV transect in the area of

positioning and locomotion behavior of these species/species groups during the same dive

The disturbance responses of codling did not differ significantly between two transects (ME10-1, ME10-3, Table 1) of a dive with the ROV Bathysaurus on the Mid Atlantic Ridge (Fig. 5a). There was however a significant difference in locomotion behavior (p<0.05). During the first transect all individuals encountered were active and mostly station holding, while several were inactively sitting on the bottom during the third transect, with less fish station holding. Drifting and forward moving occurred in both transects at rather similar

During the ROV transect VT3-2 in the Bay of Biscay roundnose grenadier and codling did not differ significantly from each other in disturbance response and vertical positioning (Fig. 5b). However, they clearly differed in locomotion behavior (p<0.005), with roundnose grenadier showing less frequently station holding and more often drifting and forward

In roundnose grenadier disturbance responses did not vary significantly between the ROV transects VT3-1 in the Bay of Biscay and ME16-1 on the Mid Atlantic Ridge (Table 1). In both cases only few individuals were recorded as being entirely undisturbed (10-21 %) and 67-87 % of all the disturbed individuals encountered responded to the vehicles at far distance. Both the locomotion behavior and the vertical positioning registered prior to disturbance responses differed significantly between the two habitats (locomotion: p=0.0005; vertical positioning: p<0.025). Roundnose grenadier occurred much higher above the bottom and showed a much higher rate of drifting on the ridge site. Station holding was frequently registered in the Bay of

c. Differences in disturbance response and natural behavior between habitats and species

**grenadier Codling False**

**0**

**20**

**40**

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**boarfish**

No response Close distance Far distance Arriving disturbed

of the Charlie Gibbs Fracture zone. Each of the three categories of disturbance responses decreased in frequency between the first and the second transect thus indicating less responsiveness. Both vertical positioning and locomotion behavior did not differ significantly between transects.

Fig. 3. Disturbance responses of (a) orange roughy during two subsequent ROV transects in the area of the northern Mid-Atlantic Ridge and (b) codling during two subsequent ROV transects in the area of Mériadzek Terrace, Bay of Biscay

The codling showed a significant decrease in disturbance responses (p<0,005; Fig. 3b) between the first and second transect of ROV dive VT1 (Table 1) on the Mériadzek Terrace, Bay of Biscay. These two transects covered different depth zones (1392-1454 vs. 1208-1228 m), the first (VT1-1) being clearly deeper. Neither vertical positioning nor locomotion behavior differed significantly between the two transects.

## **Differences between co-occurring species/species groups (Fig. 4)**

During the manned submersible transect OB22-1 on the Mériadzek terrace, roundnose grenadier differed significantly in disturbance responses (p<0.0001; Fig. 4a) from the codling. The former showed all three categories of disturbance, while the latter showed no disturbance responses at all (see also first case study; Fig. 2). Regarding natural behaviour, no differences in vertical positioning occurred, but roundnose grenadier showed significantly more forward movement and less station holding than codling (p<0.01).

During ROV dive transect VT1-1 the codling and the boarfish differed significantly from each other in disturbance responses (p<0.005; Fig. 4b) with the boarfish showing clearly less disturbed arrival and close-distance responses to the approaching vehicle. At far distance from the ROV, the frequency of disturbance responses was similar in both taxa. In addition, significant differences occurred both in vertical positioning and locomotion behavior which are dealt with at the end of the next section.

## **Variation in natural behavior and disturbance responses**

Four different comparative data sets were selected (1) to exemplify situations with disturbance responses occurring at constant or variable rates between transects/habitats or between species/species groups and (2) to analyze in detail the undisturbed, natural vertical 230 Autonomous Underwater Vehicles

of the Charlie Gibbs Fracture zone. Each of the three categories of disturbance responses decreased in frequency between the first and the second transect thus indicating less responsiveness. Both vertical positioning and locomotion behavior did not differ

**% of Activity**

Fig. 3. Disturbance responses of (a) orange roughy during two subsequent ROV transects in the area of the northern Mid-Atlantic Ridge and (b) codling during two subsequent ROV

The codling showed a significant decrease in disturbance responses (p<0,005; Fig. 3b) between the first and second transect of ROV dive VT1 (Table 1) on the Mériadzek Terrace, Bay of Biscay. These two transects covered different depth zones (1392-1454 vs. 1208-1228 m), the first (VT1-1) being clearly deeper. Neither vertical positioning nor locomotion

During the manned submersible transect OB22-1 on the Mériadzek terrace, roundnose grenadier differed significantly in disturbance responses (p<0.0001; Fig. 4a) from the codling. The former showed all three categories of disturbance, while the latter showed no disturbance responses at all (see also first case study; Fig. 2). Regarding natural behaviour, no differences in vertical positioning occurred, but roundnose grenadier showed

During ROV dive transect VT1-1 the codling and the boarfish differed significantly from each other in disturbance responses (p<0.005; Fig. 4b) with the boarfish showing clearly less disturbed arrival and close-distance responses to the approaching vehicle. At far distance from the ROV, the frequency of disturbance responses was similar in both taxa. In addition, significant differences occurred both in vertical positioning and locomotion behavior which

Four different comparative data sets were selected (1) to exemplify situations with disturbance responses occurring at constant or variable rates between transects/habitats or between species/species groups and (2) to analyze in detail the undisturbed, natural vertical

significantly more forward movement and less station holding than codling (p<0.01).

**0**

**20**

**40**

**60**

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**VT1-1 VT1-2**

**Codling**

No response Close distance Far distance Arriving disturbed

No response Close distance Far distance Arriving disturbed

significantly between transects.

**% of Activity**

**0**

**20**

**40**

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**ME10-2 ME10-3**

are dealt with at the end of the next section.

**Variation in natural behavior and disturbance responses** 

transects in the area of Mériadzek Terrace, Bay of Biscay

behavior differed significantly between the two transects.

**Differences between co-occurring species/species groups (Fig. 4)** 

**Orange roughy**

**a b**

Fig. 4. Disturbance responses of (a) codling and roundnose grenadier during a manned submersible transect and (b) codling and false boarfish during a ROV transect in the area of Mériadzek Terrace, Bay of Biscay

positioning and locomotion behavior of these species/species groups during the same dive transects.

a. Differences only in locomotion behavior (Fig. 5)

The disturbance responses of codling did not differ significantly between two transects (ME10-1, ME10-3, Table 1) of a dive with the ROV Bathysaurus on the Mid Atlantic Ridge (Fig. 5a). There was however a significant difference in locomotion behavior (p<0.05). During the first transect all individuals encountered were active and mostly station holding, while several were inactively sitting on the bottom during the third transect, with less fish station holding. Drifting and forward moving occurred in both transects at rather similar rates. No significant differences in vertical positioning occurred.

During the ROV transect VT3-2 in the Bay of Biscay roundnose grenadier and codling did not differ significantly from each other in disturbance response and vertical positioning (Fig. 5b). However, they clearly differed in locomotion behavior (p<0.005), with roundnose grenadier showing less frequently station holding and more often drifting and forward movement than the codling.

b. Differences only in locomotion and vertical positioning (Fig. 6a)

In roundnose grenadier disturbance responses did not vary significantly between the ROV transects VT3-1 in the Bay of Biscay and ME16-1 on the Mid Atlantic Ridge (Table 1). In both cases only few individuals were recorded as being entirely undisturbed (10-21 %) and 67-87 % of all the disturbed individuals encountered responded to the vehicles at far distance. Both the locomotion behavior and the vertical positioning registered prior to disturbance responses differed significantly between the two habitats (locomotion: p=0.0005; vertical positioning: p<0.025). Roundnose grenadier occurred much higher above the bottom and showed a much higher rate of drifting on the ridge site. Station holding was frequently registered in the Bay of Biscay habitat, whereas it did not occur on the ridge site.

c. Differences in disturbance response and natural behavior between habitats and species (Fig. 6b)

Deep-Sea Fish Behavioral Responses to Underwater Vehicles:

**VT3-2 ME16-1**

**4. Discussion and conclusions Deep-sea fish disturbance responses** 

the other one on the Mid-Atlantic Ridge (ME4-2-1)

**% of Activity**

**% of Activity**

**0**

**LOCOMOTION**

**VERTICAL POSITION**

**DISTURBANCE RESPONSE**

**Roundnose grenadier**

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Differences Among Vehicles, Habitats and Species 233

*.* **False boarfish Codling <sup>a</sup> <sup>b</sup>**

Close to bottom Well above bottom Far above bottom

Inactive Drifting Station holding Forward moving *.*

**% of Activity**

**% of Activity**

Fig. 6. Disturbance responses, vertical positioning above bottom and locomotion behavior in (a) roundnose grenadier during two ROV transects in Belle Isle Canyon, Bay of Biscay (left), and on the northern Mid-Atlantic Ridge (right) and (b) false boarfish (left and middle) and codling (right) during two transects, one on Mériadzek Terrace, Bay of Biscay (VT1-1) and

The underwater vehicles involved in this study elicited disturbance responses in deep-sea fishes encountered during bottom transects that can be best interpreted as avoidance or flight behavior. Clear signs of attraction to the UV's as they have been reported elsewhere (e.g., Stoner et al. 2007; Moore et al. 2008) were not observed. No longer vehicle stops and no point or selective long-term observations (e.g., by following individual fish) were conducted during the dive transects. In the studies presented here behavioral recordings were only made during

**0**

**20**

**40**

**60**

**80**

**100**

**0**

**LOCOMOTION**

**VERTICAL POSITION**

**DISTURBANCE RESPONSE**

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**% of Activity**

**VT1-1 ME4-2-1 VT1-1**

Close to bottom Well above bottom Far above bottom

> Inactive Drifting Station holding Forward moving

*.*

No response Close distance Far distance Arriving disturbed

*.*

No response Close distance Far distance Arriving disturbed

The false boarfish showed significantly more disturbance responses (p<0.05), reacting more frequently at far distances during ROV transect VT1-1 in the Bay of Biscay compared to ROV transect ME4-2-1 on the Mid-Atlantic Ridge. In the latter habitat this species was positioned slightly higher above the bottom (p=0.08 for well- and far-above bottom categories combined) and showed a significant difference in locomotion behavior (p<0.005) with much less station holding and a higher rate of forward movement. Compared to the cooccurring codling in the Bay of Biscay transect, false boarfish showed significantly less disturbance (p<0.005), a much more frequent positioning well or far above the bottom (p<0.0001) and significantly more drifting and less station holding (p<0.0001)

Fig. 5. Disturbance responses, vertical positioning above bottom and locomotion behavior in (a) codling during two ROV transects on the northern Mid-Atlantic Ridge and (b) roundnose grenadier and codling during a ROV transect in Belle Isle Canyon, Bay of Biscay

232 Autonomous Underwater Vehicles

The false boarfish showed significantly more disturbance responses (p<0.05), reacting more frequently at far distances during ROV transect VT1-1 in the Bay of Biscay compared to ROV transect ME4-2-1 on the Mid-Atlantic Ridge. In the latter habitat this species was positioned slightly higher above the bottom (p=0.08 for well- and far-above bottom categories combined) and showed a significant difference in locomotion behavior (p<0.005) with much less station holding and a higher rate of forward movement. Compared to the cooccurring codling in the Bay of Biscay transect, false boarfish showed significantly less disturbance (p<0.005), a much more frequent positioning well or far above the bottom

(p<0.0001) and significantly more drifting and less station holding (p<0.0001)

No response Close distance Far distance Arriving disturbed

Close to bottom Well above bottom Far above bottom

*.*

Inactive Drifting Station holding Forward moving *.*

**% of Activity**

**% of Activity**

Fig. 5. Disturbance responses, vertical positioning above bottom and locomotion behavior in

roundnose grenadier and codling during a ROV transect in Belle Isle Canyon, Bay of Biscay

(a) codling during two ROV transects on the northern Mid-Atlantic Ridge and (b)

**0**

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**grenadier**

**LOCOMOTION**

**VERTICAL POSITION**

**DISTURBANCE RESPONSE**

**VT3-2** 

**Roundnose Codling**

Close to bottom Well above bottom Far above bottom

> Inactive Drifting Station holding Forward moving

No response Close distance Far distance Arriving disturbed

**ME10-1 ME10-3**

**% of Activity**

**% of Activity**

**% of Activity**

**0**

**LOCOMOTION**

**VERTICAL POSITION**

**DISTURBANCE RESPONSE**

**Codling**

**a b**

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**0**

**20**

**40**

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Fig. 6. Disturbance responses, vertical positioning above bottom and locomotion behavior in (a) roundnose grenadier during two ROV transects in Belle Isle Canyon, Bay of Biscay (left), and on the northern Mid-Atlantic Ridge (right) and (b) false boarfish (left and middle) and codling (right) during two transects, one on Mériadzek Terrace, Bay of Biscay (VT1-1) and the other one on the Mid-Atlantic Ridge (ME4-2-1)
