Alex
Its no great surprise that you were asked to leave. The Bull Island is a fairly unique area (certainly by European capital city standards) and is ecological very fragile. The issue is not so much the beach area, as the sand dunes, which are held together by the Marram Grass root system. Going back more than 25 years, scramblers in the dunes area behind the beach caused a lot of damage and measures were introduced to ensure the long-term survival of the whole area as an amenity and wildlife refuge within the confines of the city. All of us benefit from this, even if bikers perhaps feel hard done by. The fact that you were asked to leave the beach area seems a bit harsh, but if this was summer-time bike activity beyond the stones would be threatening beach nesting birds in the area - as do hoards of sun-bathers, but such birds can generally distract a nosey kid if they stray too close - not so a bike(r). At the end of the day, rules are rules, and in this case the potential cost of damage and disturbance has led to a blanket no-no being put in place!